Sorry for the late reply, I hope someone will read this
Actually the GPU temps are pretty stable. Normally (not running any games) the temp oscillates around 40-45°C, and while playing Skyrim, L.A. Noire or other games with high requirements, the temp rises to about 60°C.
And I don't really like the idea of a fresh winstall, as I have no backup drive, and don't want to reinstall all the programs and such (I'm a really lazy person). But I don't really think this is the issue, I have installed Win 7 pretty recently, a couple months ago I think.
Do you maybe have any other suggestions how to find out what is wrong, or to improve the situation / eliminate the problem?
Thanks in advance!