I have a Radeon HD 4850(XFX), and I was using it in my computer for a while, and it worked perfectly in Windows and Linux. Then, I took a Radeon HD 6750 and dropped that in for a while to test it out. I didn't like it's displayport and didn't have an active adaptor, so I pulled that out, and put my 4850 back in, but now that doesn't work. I've fixed the drivers, and I'm pretty sure they're not the problem as it crashes in both Linux and Windows.
Both cards were plugged into a PCIe X16 slot, and with a 6pin PCIe power cable from my 500W PSU.
Windows: Boots, and works for a while(like 2-4 minutes), then displays something funny like an all white, all black, or random noise. One of the times it crashed, I heard the GPU fan kick on and it wouldn't stop.
Linux: Boots, but won't start Xorg. Complains "The Display Server has been shut down about 6 times in the last 90 seconds. It is likely that something bad is going on."
Tail of Xorg.1.log:
[246.325] (II) SELinux: Disabled on system
[246.335] (II) AIGLX: Screen 0 is not DRI2 capable
[246.335] (II) AIGLX: Screen 0 is not DRI capable
[246.339] (II) AIGLX: Loaded and initialized swrast
[246.339] (II) GLX: Intialized DRISWRAST GL provider for screen 0
[246.376] (II) RADEON(0): Setting screen physical size to 270 x 203
[246.376] (II) RADEON(0): Allocate new frame buffer 1024x768 stride 1024
Tail of Xorg.0.log:
A bunch of things ending in "Success" which I've omitted, and:
[63.410] (II) RADEON(0): RADEONRestoreMemMapRegisters():
[63.410] (II) RADEON(0): MC_FB_LOCATION: 0x003f0000 0x00df00d0
[63.410] (II) RADEON(0): MC_AGP_LOCATION: 0x00000000
[63.420] (II) RADEON(0): avivo_restore !
[63.429] Server terminated with error (1). Closing Log File