My Radeon HD4870 worked just fine few weeks already, pretty heavely OCed on Q9450 host.
But today after Vista restart desktop was completely frozen, no response from keyboar or mouse due ~min and screen updates also one per ~minute or 2.
No Vista updates was installed last few days, no changes in opt app config.

Could such behavior signal about card overheating or there are another symptoms?

Maybe something changes in tasks sent by project ?
Any other suggestions?

I did another OS reset and after reboot all works just fine as was before, no delays in screen refresh or mouse movements at all.
What it was?....