Combination software/hardware woes

i've recently been having some issues with my pc.

hardware:
gigabyte ep-45-ds3r
q6600
asus 4850 512mb
4gb ocz ram
corsair 650w psu

i was using xp64 for the past few months, and due to driver issues (and a bevy of other problems), i decided to switch over to 64-bit vista when i added a new hard drive.

the os install went fine, but i started encountering errors when i attempted to get my video drivers in order. the computer was operating fine without the drivers, but once drivers from the manufacturer were installed, the computer began acting weird.

the computer entered into a cycle where it would reach as far as the vista loading screen, and then it would shut off. it was stuck in this cycle until i booted into safe mode and removed the drivers.

once it was without drivers again, it was able to function without issue.

things that i tried:
flashing the video card bios
flashing the motherboard bios
memtest passed
hdd test passed
tried drivers from asus, ati, and third party - none worked.
disabled the .exe dealing with the dynamic energy saver
reinstall the os (multiple times)

i'm at a loss. anyone have an idea as to what could be the problem?

Are you sure that you have the 64 bit drivers?
32 bit wont work.