"If playing with video driver versions hasn't helped, make sure the box is not overheating. Try removing a side panel and aiming a big mains fan straight at the motherboard and GPU. Run it like that for a few hours or days - long enough to ascertain whether cooler temperatures make a difference. If so, it might be as simple as dust buildup and subsequently inadequate cooling." - H2SO4

From this link ( http://forums.amd.com/game/messageview.cfm?catid=260&threadid=104677&enterthread=y )(link is dead, similar topic here: https://community.amd.com/message/2648813#comment-2648813 ) :

The following hardware issues are examples that can cause a TDR event:
- Failing overclock on CPU or GPU (stop overclocking)
- Bad sector in memory resulting in corrupt data being communicated between GPU and the system (either video or system memory) Memtest and video memor stress test: http://www.carrona.org/hwdiag.html
- Corrupt hard drive/windows install resulting in corruption to the system registry or the page file (Hard drive diagnostics: http://www.carrona.org/hddiag.html , reset your pagefile:

Use this technique to "reset" your pagefile:
a) Go to Start...Run...and type in "sysdm.cpl" (without the quotes) and press Enter. -Then click on the Advanced tab,
-then on the Performance Settings Button,
-then on the next Advanced tab,
-then on the Virtual Memory Change button.
b) In this window, note down the current settings for your pagefile (so you can restore them later on).
-Then click on the "No paging file" radio button, and
- then on the "Set" button. Be sure, if you have multiple hard drives, that you ensure that the paging file is set to 0 on all of them.
-Click OK to exit the dialogs.
c) Reboot (this will remove the pagefile from your system)
d) Then go back in following the directions in step a ) and re-enter the settings that you wrote down in step b ). Follow the steps all the way through (and including) the reboot.
e) Once you've rebooted this second time, go back in and check to make sure that the settings are as they're supposed to be.

and run the System File Checker

SFC.EXE /SCANNOW
- Go to Start and type in "cmd.exe" (without the quotes)
- At the top of the search box, right click on the cmd.exe and select "Run as adminstrator"
- In the black window that opens, type "SFC.EXE /SCANNOW" (without the quotes) and press Enter.
- Let the program run and post back what it says when it's done.

- Over heating of GPU or CPU again resulting in corrupt data being communicated. (Point a house fan at the video card, take temperature readings from the card with an IR detector (or your finger - but be very, very careful!!!))
- GPU failure due to any sort of issue from insufficient power (VERY common) to heat. (check the power leads, use a multimeter to check the power output, try another, more powerful PSU)

The following software issues are examples that can cause a TDR event:
- Incompatible drivers of any sort (either GPU, sound, etc) (Original link is dead: http://www.microsoft.com/windows/compatibility/windows-7/en-us/default.aspx ) (not a real good link, but it does have compatibility info: https://www.microsoft.com/en-us/search/result.aspx?q=compatibility+center&form=apps )
- Messy registry (I doubt this and don't approve of registry cleaners)
- Known vista issues resounding around multiple displays, aero, dreamscape, and various display drivers. (none known for Win7 - but in early to mid-2012 there were some reported issues w/ATI drivers)
- Known vista issues that sometimes cause corrupt information to be sent to the video card from system memory (will be addressed completely in SP2, has had various fixes applied since vista's release) (none known for Win7)
- Bad direct x files (uninstall, then reinstall DirectX)
- Bad system files (System File Checker - was run above)
- Bad driver (some drivers will cause an event due to internal bugs, however these are not nearly as common as many think due to all of the previous things causing the same symptom) - (remove all 3rd party programs and check to be sure drivers aren't loading. Then install only the necessary 3rd party stuff, and ensure it's the latest version and that it's compatible with Win7)