Sapphire 4850 Won't Display A Picture

I purchased my new computer on Christmas 2008 due to the sales they had that day. When I first got it, it work perfectly fine without even downloading the drivers. I'm a developer for a game and I use various software needed for graphics editing. I play a 10 year old game (Sony's Infantry) almost everyday on average for 1 to 3 hours a day and my system temps are pretty normal. Around 40-50C temps when playing. I use compressed air every 2 weeks and my case is nice and tidy so there's no dust bunnies or anything of that sort.The problem arose during the month of August 2009. There were no artifacts or blue screens or anything like that. The computer would just suddenly turn off on its own and when I tried to power it on, it did not display a picture. I saw the CPU fans spinning, the HDDs were running, all the cables are connected properly, the video card (sapphire 4850) fan was on and there's 1 beep code.

I asked my friend to borrow his old 8600GT and my computer worked normally. He suggests that my PSU may not be supplying enough juice to the GPU. I thought it might have been the mobo. But my friend is more knowledable than I am. I ended up buying a new PSU. The PSU ended up not solving the problem. Then I buy the same exact card that gave me the problem and a new motherboard and installed the drivers.. that didnt do it either. With basically a brand new computer minus the RAM, I end up with the same results.

Original setup:
Intel Q6600
Sapphire ATI 4850 HD
Asus P5E
Antec 500W
G.SKILL 4GB (2 x 2GB) 240-Pin DDR2 SDRAM DDR2 800
Antec 500W Continuous SLI Certified CrossFire Ready 80 PLUS Certified
Windows 7 x64
Windows Vista x64

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