Ah, you have the 280 overheat problem. Note that those card (the 280, 260 etc) run perfectly fine at those temperatures other than the occasional hiccup. I'd personally go onto a more techy forum and ask around there to see if there's anything you can do to lower the
OH OF COURSE
It's because the fan isn't spinning at top speed or something like that, I'll go research it. (The whiteout is caused by your GPU, by the way.)
The slow to close down thing most likely is because there is a background program that's running and refuses to shut down when Windows is telling it to.
EDIT: What you could try:
1) Get the latest firmware. (Just saying this for the sake of caution - and people on the net randomly stumbling on this thread.) Check your temps again after the computer's been running for a while.
2) If it's still running v. hot while under load, you're going to need to be a little cautious. With the newest nvidia drivers installed, install their customisation tool nTune. http://www.nvidia.com/object/ntune_5.05.54.00.html
(latest version at time of writing)
3) Go into your graphics options, then you need to search around inside for options to turn up your fan speed. Turn it off automatic and then up to 100% (ie the max) speed.
4) Cooler GPU!
(Just as a warning, it may also sound like a plane is taking off. Customise your fan speed to where it's quiet but no longer whitescreens.)
Of course, it could be a case that the card has been overclocked...