Almost 2 months later I got around to take my motherboard back to the shop and had it swaped for a new 880GM-UD2H. They confirmed the old one was problematic, probably something to do with the on-board graphics card.
My system now seems to be working fine, I have been running it for two days.
The only thing is that even though I now have 8 GB of RAM installed, Windows 7 64-bit shows a total of only 2813 ... The BIOS detects all 8GB.. a new issue to solve.. hurray. Except if someone has a quick fix for this I will have to dig in the forums again
But anyhow thanks for all your help!