I have had very few issues with Skyrim, a couple of crashes early on and as far as I can tell no quests have been bugged.

But twice now I have had what you would call a CTD, the game reverts to a full screen bordered window but the whole centre looks clear, I can see my desktop but I cant click anything.
Skyrim is still running I can hear it, I just cant see it.
Alt-Tab does nothing, all I can do is CTRL-ALT-DEL and hit task manager.

What happens as soon as I click task manager is really weird.
Skyrim comes back full screen, no border just as it was before the crash.
Alt-Tab now works and I see task manager running so I close it and I go straight back to the dead window.
Open task manager again and Skyrim comes back.

I can leave task manager running and play for hours without any more trouble and once I shut skyrim down I can close task manager and fire Skyrim back up no problem.

I have no mods installed.

Try Alt+Tab, then Win+Tab or Alt+Tab twice. Seems like you have to switch focus to TESV.exe twice for it to come back all the way.

The only thing that does anything when it does this is CTRL-ALT-DEL and as soon as I click task manager Skyrim comes back as if nothing happened, I dont even get to see task manager until I ALT-TAB out of Skyrim.