Sorry to say, but I think you will find you are totally out of luck if you can't find the Product Key.
Is there any chance you still have the original purchase confirmation email? The product key would be there. Use the search feature in your email program.
The fundamental problem is that MS expects you to keep your own records of your product key. If you don't, MS won't help you. So you can try that Parth provided, but I don't think it will help.
In THEORY, the switch to Win 10 (personally I won't call it an upgrade from Win 8.1) is supposed to carry over any programs that work. In practice it seems carrying over Office 2010 has been hit or miss. It worked for some people but not for others. After
the initial "upgrade" you had a 30 day time period when you could "back out", return, to the original version of Win. During that time you could have used a tool to "extract" your 20101 product key from that "old" version. MS is treating this as a bonus
opportunity to make more money by forcing people to buy new copies of Office programs.
When you buy Office programs online, that purchase is recorded with your email account. But from what I understand, they only keep that record for a max of 5 years, so it MAY be there, but probably not. Log in to your MyAccount page and look around there:
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Services & Subscriptions: Office 365, OneDrive, Outlook.com
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Payment & Billing
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Devices
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There is an absolutely tiny chance that you can still find that key. It MAY still be in your "recycle bin". Open the recycle bin and look for the file "Tokens.DAT". If you find it, restore it and use one of these tools to extract the keys.
PS: you should extract your Office 2010 key and record it somewhere it won't get lost in case you need it again in the future.
Tools to Extract Product Key
http://www.7tutorials.com/how-recover-your-lost-windows-7-or-windows-8-product-key
http://pcsupport.about.com/od/productkeysactivation/tp/topkeyfinder.htm 2015 10 01 - Review 22 Free Tools
You can use any of the following tools to extract the Product Key from you computer. These tools report on many installed programs on your computer, not just Office.
PS: you should keep a copy (printed and/or file copies on external storage devices) of the report(s) generated by these tools so you have all of your
product keys / registration numbers available for future re-installs
FYI: I (Rohn) have not tested these tools in Windows 8 (just haven’t had an excuse to make/waste the time), but I don’t expect any problem. The underlying
mechanics of Windows 8 are essentially the same as Windows 7 if you ignore the Metro User Interface. Think of metro as “lipstick on a pig”. The pig is not changed by adding a little paint on the surface.
Normally you have several resources to find your Retail Product Key.
O
Your original package or purchase confirmation e-mail
o
Online download account
o
You can extract the Product Key from the machine itself
o
Image copy backups of system with Office installed
o
Activation backup utilities From what I’ve read, MS uses a file called
TOKENS.DAT to store encrypted product activation keys:
C:\ProgramData\Microsoft\OfficeSoftwareProtectionPlatform\Tokens.DAT
C:\Windows\ServiceProfiles\NetworkService\AppData\Roaming\Microsoft\SoftwareLicensing\Tokens.data
C:\Windows.Old\ProgramData\Microsoft\OfficeSoftwareProtectionPlatform\Tokens.DAT (if you did an in-place Windows Upgrade)
NOTE: Do not expect the Windows.OLD folder to be there until you delete it. Many people have complained that windows 8 and 8.1 automatically delete
it WITHOUT WARNING http://answers.microsoft.com/en-us/windows/forum/windows_8-files/windows-8-has-deleted-my-windowsoldprogramfiles/dbdf75c0-09d9-4992-b8eb-d9fac3efe9b8?page=2
After you extract the Product Key, make sure to write it down and keep it in a safe place. Burning a copy of the installation file to a CD would also be a good idea if you don’t have the installation disk.
NOTE: OEM (factory install and activated) licenses use a different key than the one reported.
Only the factory can use the PK from the original factory activation. You would have been provided with a separate piece of paper with a Product key for reactivation.
Belarc
http://www.belarc.com/free_download.html
- not only does Belarc
extract product keys, it reports on a WHOLE BUNCH of other stuff you want to know. Printing the report, or saving it is probably a good idea.
Win 95-Win8, V8.4
NOTE: I tested version 8.4 on Windows 8.0. It reported my Office 2003 2007 2010 product keys correctly.
BUT for Office 2013 Pro Plus (local install) it did NOT report the key! Gosh Darn!
It reported: 00215-95000-26121-AA381 (Key: ends with G8YGX)f,g
(the “ends with” is correct)
Superscripts f and g say:
f. The full product key is not stored on this computer. However, the characters shown uniquely
identify your product key.
g. You can have Windows save the full product key using the procedure at
http://www.belarc.com/msproductkeys.html.
NOTE: The process described in the link in “g” is good for Office 365, and MAYBE (I can’t confirm) online
purchases of Office 2013. It does NOT work for Office 2013 Pro Plus! (which I have <grin>)
License Crawler
http://www.technibble.com/license-crawler-find-product-keys-in-the-registry/
98 (Office 2003, 2007 , 2010 , Win Vista)
I tested V1.37.463 on Win 8.0 it reported Office 2010 correctly, did not report 2007 or 2003.
The “serial number” aka Product Key reported for
Office 2013 Pro Plus (local install) did NOT agree with my documentation of key used!
SterJo Software Key Finder.
http://www.sterjosoft.com/list/ - Confirmed to work on XP through Win8, Office XP/2002 through 2010
Win XP to Win 8, Office XP to 2010.
I tested V 1.7 on Windows 8.0. It reported my Office 2003 2007 2010 product keys correctly.
The “serial number” aka Product Key reported for
Office 2013 Pro Plus (local install) did NOT agree with my documentation of key used!
Abelssoft MyKeyFinder
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http://www.abelssoft.net/mykeyfinder.php -
I tested MyKeyFinder 2014 Free on Windows 8.0. It reported my Office 2003 2007 2010 product keys correctly.
The “serial number” aka Product Key reported for
Office 2013 Pro Plus (local install) did NOT agree with my documentation of key used!
Sorry, I have not had opportunity (aka need) to test Win8 and Office 2013 on these various tools:
Magical Jelly Bean
http://www.magicaljellybean.com/
is free, supports 300+ programs V 2.0.8- Office 2003 OK, 2007 OK, 2010 na, Win Vista Wrong). They also have a paid Recovery Keys, support 4500+ programs
V 2.0.9.8
http://sourceforge.net/projects/keyfinder / -
Enchanted Keyfinder Beta Portable- Win (9X, ME, NT/2K/XP, Vista, Win7), MS Office (97, XP, 2003, 2007, 2010), Recover key for 484 other software and counting
http://www.nirsoft.net/utils/product_cd_key_viewer.html
Nirsoft ProduKey V1.45- Office 2003 OK, 2007, 2010, Win Vista)
V1.62 Win 98 to Win 8. Office 2003-2010
ProduKey
may be able to extract product key information from a file saved externally. This is useful if you’re trying to get the key details from the backup of a now defunct machine. Try the /Regfile option.
<snip>
After installing on my system, I ran the program
à AS ADMINISTRATOR
ß and then
clicked on File à Select Source. Once in this menu it
may appear a little overwhelming, don’t worry it’s not that complicated and your not going to break anything else. Select the circle next to “Load the product keys from external Software Registry hive”. Now from here you may have to browse to a slightly different
location depending on where your windows.old folder is located, but you want to basically browse to the following and open this file:
C:\Windows.old\Windows\System32\config\RegBack\SOFTWARE
After opening this file select ok; you may have to wait a few minutes for it to load the hive and give you your keys, but if they’re there you should see them and be able to fresh install your MS Office.
Please note that this did work for my Office 2007, it also gave me my Vista Home & Personal Key, and Internet Explorer... lol! I hope this helps someone else too! And remember backup before you do any upgrading/downgrading/or
destruction to you PC.
</snip>
http://www.winkeyfinder.com/download.php
(Office 2003 , 2007 , 2010 , Win Vista )
V 1.73 final Win 98 to Win 7 (and more?) 32bit, Win XP to Win 7 64bit Office 2000 to 2010 32&64-bit
http://www.recoverlostpassword.com/products/productkeyrecovery.html (trial)
Product Key Recovery 2007 2010 2013
NSAuditor Product Key Explorer
http://www.nsauditor.com/product_key_finder.html
Win XP to Win 8.1, Office 2003 to 2013
V3.6.3 Must buy to run. Free trial only shows partial key