I recently went out and bought a GTX 480 (SC version from EVGA), and I'm having some troubles with it, and want some opinions.
Problem : Computer screen goes black for about 1-2 seconds randomly (Can be 3 times in 1 minute or 1 time in 30 minutes), more common under load, but still happens when idle.
Notes : Screen works fine, occurs more frequently if overclocked further, card produces no artifacts and runs around 95 Degrees at load, Memtestg80 shows no faulty ram, re-installing newest drivers didn't help, tried on another O/S of Windows 7 on a different partition, and same problem persists.
Mobo: ASUS M4A79 Deluxe
Ram : OCZ Reaper DDR2 800mhz 4gb
GPU : EVGA GTX 480 SC
CPU : AMD Phenom II 1055t @ 3.78ghz
Driver : Latest NVidia driver (258.96)
O/S : Windows 7 64bit
Programs running : EVGA Precision, PowerISO
Monitor : Sony Bravia 40"
Assuming that your PSU is up to task (you don't mention what it is) and the DVI or HDMI cable is good, then that sounds like the card might need an RMA.
Here's the funny thing... I had this same model before, but returned it to the store due to the memory not resuming full speed after it throttled itself at idle. In turn I got a plain 480 by evga, which had this same problem. I returned that card because I figured it was hardware related, and got this SC with this same problem. Ironically, I find out that the reason my memory wasn't returning to normal clocks was due to a program from EVGA called E-LEET. God I wish I had my original card back.
Side note : Oh yeah, my PSU is an Antec 1000w... More than enough power is getting to the card.