HD Radeon 5770 Compatibility

I am planning to get a new graphic card for my old pc, since my XFX9800GT recently got fried( i am just assuming, i am not sure how to check this.)

This is what happen:

I haven't turn off my computer for around 14 days straight, and i have a pretty crappy case for air float, My GPU stays at 6x during idle and reach peek at around 8x during gaming with higher setting.

2 days ago, i was running L4D2, (my comment doesn't even need a good graphic card for this sighz...) but suddenly my screen froze, and my system is not responding. so i restarted my computer, and when the computer goes back on, the resolution becomes 800 x 600, and maximum i can change to is 1680 x 1050, (which is less than what 9800GT should support) so i run dxdiag on window. on the display tab in dxdiag, it doesn't seem to detect any display/GPU device. After that so i checked device manager, it has a exclamation mark on both 9800GT in the display adapter tab - Code Error 43 and another exclamation mark on Coprocessor in Other device tab - Code Error 28

Here is the list of things i tried to do.
-restarting my computer
-Updating 9800GT and Coprocessor
-reinstalling my computer
-Checking BIO when the computer boot
-Checking bio on my computer
-Tried to reinstall the driver, but a message pop up when i run the setup from disk. [The VGA Detected seems not XFX's product. Please go to www.nvidia.com to get the driver for the other NVIDIA VGA] but this installation should work since the disk came with the 9800GT


Things going to do:
-Getting a new PCI cable and/or replacing the 9800GT with Radeon 5770. but before that i have to check the comparability


Is there a way i can fix the 9800GT, or should i just buy a new graphic card?

If i should get a new graphic card, then.....
Two questions i would like to know are:
A)
Is the motherboard XFX MIA78S8209 compatible with Radeon HD 5770?

B)
Will my power supply be enough for the Radeon HD 5770?


my spec are:
Motherboard: XFX MI-A78S-8209
RAM: 4GB
CPU: AMD Athlon 64 X2 6000+
HHD: Seagate ST3500320AS ATA Device
Power supply: 650W