Internet videos (streaming) freeze

My System:
Win 7 Ultimate x86, Pentium D 945 3.4GHZ, DDR2 533 2GB RAM, geforce GT610 1GB , Motherboard Chipset ATI Radeon Xpress 200.
DXdiag shows no errors.

Recently, every video that I play online, in any sight , in any format (Flash or HTML5) , freezes after about 30 seconds. The voice is also frozen, creating a loud buzzing. Windows is completely frozen as well , no response to mouse or keyboard. After about 30 seconds it releases, but freezes again after a while. This also happens with online flash games.
The original driver version was 314.07 , I tried 320.49 (the latest stable) and also the latest beta 326.19. I also rolled back to 314.22 - to no avail. Problem continues.
Flash player is latest version available (11.x.x).
All drivers on system updated to latest versions.
It does not happen with the onboard ATI video card.
This did not happen until now.
It appearse to be a problem with the geforce driver. Occasional, after the system releases I get a balloon message in the system tray: Display driver nvlddmkm stopped responding and has successfully recovered.

The problem is not specific to a sight (youtube , dailymotion etc), nor to a browser (IE, Chrome, Firefox, Opera).
I have no problems with the same videos downloaded as mp4 or flv.
I tried Passmark Burn-in - no errors at all.
It only happens when streaming.
Microsoft troubleshhoter found no problems to fix with codecs.

I saw many posts going back to 2009 with this phenomena, but no real solutions.

Anyone has an idea what is going on and how to fix it?

Thanks