That BlueScreen is a pleasant surprise in its informativity: It clearly says that ati2dvg has done something and explains that the driver has got stuck in an infinite loop which may indicate a problem either in the device or its driver.
You're not telling which Windows version is in use, but any of them can be started in SafeMode by clicking F8 at startup. From there within go to
Start -> All Programs -> Accessories -> System Tools -> SystemRestore and look what the latest restore point would remove. If it says "driver update", you've found the reason for the bsod. In any case, rolling back to a previous state doesn't affect personal files, only things that have been installed after the Restore Point, so it's a good starting point.
If that doesn't help, un- and reinstalling the driver is the next step. The install packages of all ATi drivers used in the computer will remain in C:\ATi even after uninstalling the driver from within "Programs and Features", so no download is necessary, just choose the right one from there.
If the problems don't go away, running a CHKDSK wouldn't hurt,
how-to here.
If all this doesn't help, it is starting to sound like a hardware issue, either the GPU or PSU is failing.