4850 Crashes "no signal"

Specs:

Intel e8400
Gygabyte EP35-DS3R
HIS Ati Radeon HD4850
Antec Truepower Trio 430 W
Mushkin 2 GB DDR2 ram
WD 320 GB
DVDrw

I recently noticed, upon installing games like Fuel, Bionic Commando or Call of Juarez, instant crashes. Immediatelly after entering the game or 2-3 minutes later, the PC crashes, i get "no signal, check cable" on monitor and sound keeps on going sometimes, other times enters a loop and PC restarts.

I reinstalled windows (XP), same thing. I used an older catalyst (8.6) instead of 9.6 or 9.7 and one game doesn't crash (Bionic Commando), the others do. I ran video card stabity test and it crashed about 1 second after it started.

I never experienced problems in games like Age of Empires 3, Assassin's Creed, Fallout 3, World in Conflict, Far Cry 2, Crysis (although in Crysis a crash would occur about 1-2 hours after playing).

I tried disabling Catalyst AI and nothing. THe board runs 80 degrees idle and 90-95 in games (it's the first version of the HIS, no ICEQ4). Yet I manually set the speed of the fan to 50-80% and the temps went to 60 degrees, but no effect on th crashes.

One thing that worked: underclocking the memory clock from 993 to 900. I can enter the game and play but I don't know for how long. DIdn't play for hours to check.

Any help I will apreciate.

No, not at this time...

No nvidia ... no OC ...it's not the temperature .... 2 GB of memory is sufficient for any game I have played. Never saw a game with more than 2 GB ram recommended .... except gta 4 on vista; i use xp.

BUMP
OK, i've changed the PSU to a enermax 500W eco 80. I sent the card to the manufacturer and he said there wasn't a problem with it, though i don't know how deep did they test it.
Nothing works. I tried swithching to vista and the crash occured less frequently.
Still, why does underclocking the memory clock to 900 Mhz work?

I'm out of ideas here ... it's not the temp, it's not the psu ... what the he** could it be?

PLEASE HELP!


LE: i also tried setting the PCIe from BIOS to 100 but it didn't work .... tried disabling AI from catalyst, but it also did not work.