Windows 7 computer cannot work with Windows 8 phone - help needed to install the proper windows phone usb-drivers

Computer history
A few months back my Creative zen mp3-player suddenly was no longer recognized by windows 7 computer (about two years of age). I didn't do much to solve this problem at the time as all other USB applications (sticks, external hardrive) still worked and I could use a SD-card to transfer music and other data.

The problem
However last Friday I received my new smartphone Nokia Lumia 620. One of the reasons for buying a phone with Windows 8 was the presupposed compatability with my Windows 7 computer. And I was eager to finally transfer music and other data easily. Unfortunately, the phone wasn't and still isn't recognized by computer. The problem lies with the computer, not the phone, for a much older Windos XP computer did recognize the device. The USB-gates are all working fine. The device is recognized as a RM-846|Nokia Lumia 620, but the computer is unable to install the proper drivers.

My own attempts
Windows update says there are no further updates available. I turned of my firewall, and have tried to install the drivers, both automatically (Code 28) and manually. I have downloaded Microsoft - Other hardware - Windows Phone USB, from the Microsoft website but even within this folder, windows says it cannot find any drivers. The use of Microsoft fix-its also has not helped.

I have done all that the self-help websites recommend, but now I am stuck. And I really want this to work properly. Friends tell me not to bother and just buy a micro-SD, but why should I? I want this to work as it is supposed to work and not spend money on a second-rate solution. Pleas help me crack this nut.