Windows won't activate?

How many times can you activate Windows 7:
http://answers.microsoft.com/en-us/windows/forum/windows_7-windows_install/how-many-times-can-i-activate-windows-7/b56970fd-a655-4b8b-8a21-c9e8dbb1f818

Please run the Microsoft Genuine Diagnostics Tool then copy and paste the results in a reply here for further analysis:
http://go.microsoft.com/fwlink/?linkid=52012

Microsoft's Response: Microsoft is committed to helping prevent software piracy, which often results in end users being the victims of software counterfeiters. Counterfeiters abuse product keys to create fake software packages and distribute these to the public. These packages are not licensed, do not have Microsoft support, and can also include dangerous malware and spyware.

Recently there have been a few keys purchased from auction sites showing up here as non genuine, they appear to be connected to this HROnline code HrOnline: 0xC004C4A2. If you purchased a key from EBAY please realize that the seller may have sold that key to multiple people resulting in that key becoming blacklisted. These keys were never meant for resale, they were meant for software development or evaluation depending on the program they were obtained through. If you purchased one of these keys and it has become non-genuine with the above code you may need purchase a new license for windows 7. Attempt to validate by going to www.microsoft.com/geniune and follow the links provided to repair windows.

Added note. You only have a limited amount of time (45 days I believe) to file a claim with the auction sites. Stay away from these keys, if you purchased a key that has turned non-genuine and are within the 45 days of purchase file a claim. There are legitimate software vendors on auction sites but if it sounds to good to be true then don't buy it.

 It seems you are running a license intended for a particular channel. Yes, you might have a perfectly looking hologram disk, but this doesn't mean the license is legitimate since its easy these days to make hologram disks. Persons who work at the factory can secretly create hologram disks they resell on the black market or purchase press machines to do the job.

Learn more: http://www.msnbc.msn.com/id/40045602/ns/technology_and_science-the_new_york_times

EDIT: Additional information

Things to watch out for.

Lately there have been several reports of instances of blocked MSDN keys packaged with legitimate looking media. I can't stress enough to save your packaging, media and reciepts, if you purchase software such as this seek recourse with the store you purchased it from and report it to www.microsoft.com/piracy 

If you have purchased a key, with or without DVD's or packaging from EBAY or any other person or vendor and believe it may be an MSDN key because your key has been blocked you can check a few things yourself, if you received your key with the physical product go to www.microsoft.com/howtotell and verify your product however some counterfeit software is so convincing you may not be able to spot it as such.

To check your PID press the win key and pause at the same time, or open system properties through the control panel, scroll down to activation section and look at the PID It will look something like this 12345-067-1234567-54321, the portion you are interested in is the three digit section, if it matches or is within one or two digits of the examples below you probably have an MSDN key.

065, 066, 067, 068 for Ultimate, 220, 221 area for Pro and the 230, 231, 221, 232 area for premium, there are probably others but they should be close to those posted

About MSDN or TechNet Product Keys
They are genuine Microsoft product keys, they are actually retail licenses, but it is intended for a particular product channel either the Microsoft Software Developer Network (MSDN) or TechNet for IT Professionals who pay a subscription fee. The main purpose is for evaluation purposes. The great thing about them, unlike trial Microsoft software, MSDN or TechNet keys don't expire. Because the agreement under which the subscription is provided is a single license, none of the software should be distributed outside of it. Even though its $50,000 worth of licenses, it is for one person only to use and no one else. Unfortunately, regardless of the licensing terms, persons still abuse the program, either giveaway product keys or resell it on auction sites. Microsoft licenses it in good faith that customers won't do so, but I guess human nature wins out.

In your case, what probably happened is, you bought an MSDN licensed key, which carries up to 10 activations unlike full packaged retail licenses which only carry 1 activation. The person who sold it to you probably sold it to 10 other persons. Somewhere along the way, one of those persons might have installed it on a second system, activated it, because it went past 10 activation threshold, Microsoft detected it that it was being abused and blocked the key from further use.

Validate Now:
You can confirm that your software is genuine now. It’s quick and easy.
http://www.microsoft.com/genuine/validate/ValidateNow.aspx?displaylang=en
Click the 'Validate Windows' button, if the validation check fails, then click on the 'Get Genuine' button to get a WGA Kit.