Stuck in 16 bit colour?

[badger]

Got a weird problem that started last night. My Windows 7 install seems to have got itself stuck on 16-bit colour mode, or something like it. White areas, like this text box and, say, Google homepage, are displaying blue cross-hatching or dithering and the same pattern is showing up on icons and graphics all over the place. However high-res images seem to display fine and games run okay with little or no dithering visible, and I can enable transparency in Aero which I wouldn't be able to do if it was on 16-bit colour.

I've reinstalled NVIDIA drivers twice (Asus GTX 560 card), both clean installs, and all the settings I can find in Windows and NVIDIA control panel say it's running 32-bit colour.

Any ideas what could have caused this? My next step is to try reinstalling Windows but I'm reluctant to do this because it's a pain in the arse and I have no idea what caused this issue so don't want it to happen again.

[Ginger-Menace]

have you tried a different cable/monitor?

[daveleebond]

system restore from the last point?
go to a cmd prompt and try 'sfc /SCANNOW to repair any corrupt files.

[Pilgrim_uk]

You might have switched on the accessibility features by mistake.

[badger]

Looks like it's the monitor, had to borrow one but the problem is gone. Now my monitor isn't even powering up.

RMA it is.