Today! I built a new system with Gigabyte P45-DS3R board.  
 
After installing VGA driver for my 9800GTX, I can not enter into Windows Vista. System hangs up ..only black screen. Try 9800GTX VGA card on my old system, it works fine. strange!  
 
Does anyone meet same problem???
 
HELP me, please??

What's the psu & how old is it?

Hello! I use ENERMAX 600W SLI ready power supply, about 1 year old.
 
I have tried to reinstall CPU, memory and VGA card. also change power supply to my friend's big 750W power. still no luck. black screen.
 
test all devices on my old board, no problem.    

Ok, is there any light/fan activity during the black screen? Try each stick of ram in each of the slots. Once the pc posts, go to bios & up vdimm to 2.1v or specs.

Ok, your problem is that your bios is out of date.
 
On startup, hit tab to see the POST.. Your probably running F4 bios, thats what mine came with.
Update it to the latest one which is F6.  This fixes the problem.
 
I just built a new system and nearly fainted when this happened, since i thought my new
gear was dodgy...