I've had a quite strange graphics errors occurring for a couple of months with my 3 year old ATI 4870. There are certain games where this happens on a regular basis, for example after starting AikaOnline and playing it for about 10 seconds (i.e. with the system still being relatively cold), but more recently also when for example playing Lord of the Rings Online and Alt-Tabbing into something with video content, for example CNN or so. This makes me wonder if the card is on the way out.

Here is what happens:
The screen kind of garbles up, little rectangles of about 3*5mm are appearing on screen in a strange chessboard-like pattern, these rectangles are filled with what appears to be the graphics content of the next screen to be built up by the graphics card. So you basically see a frozen screen interspersed with small rectangles appearing to belong to the next screen to be shown. (bit difficult to explain, sorry, I googled for a screenshot showing something similar, but couldn't find anything)
So the screen is completely frozen, there is some brief harddisk activity and sometimes an attempt to access the dvd-player for about 5 seconds, also any music plays on for that time. After that the computer is frozen completely and can only be restarted using the reset button (which is highly annoying as my RAID1 array is then spending hours on verify status, slowing everything down.)

So, the fact that I couldn't find anything on the web in terms of screenshots or explanation leads me to believe that this might be a Hardware fault and that it may be time for a new card (drivers are regularly updated, Windows 7-64, Intel Quad 6600, airflow in comp is good (Overclockers built comp), dust removed)

I just would hate splashing out for a new card, only for this to appear again. Also I thought it may be safer to go for a NVIDIA card, just in case there were any hidden driver gremlins interacting with the ATI.

Thanks for your help and advice

edit: got the age of the card wrong

Have you got any warranty left on it?

its strange ive seen a few posts in graphics cards the last few days about system slow down and graphics glitches. Ive had the same thing happen to one of my computers last week. An I5 build with a ati 5770 graphics card, i thought it might of been the 11.8 cat drivers but putting the old drivers didnt help neither did cleaning out the fans and CPU-Z reads everything at the right levels...its all very weird.

Re warranty:

Don't think so, bought the prebuilt-overclocked setup in November 2008

Do you get any issues outside of windows, i.e. during POST and boot sequence? If so then you can be pretty near 100% sure it's a hardware failure - if not, you might yet find a software fix

Try removing all overclocks? Especially GPU OC

No issues outside, and removed overclocking, still the same happens.

Thanks for comments so far, any more ideas?