Weird 4850 crashes

So I've been getting these weird crash's in games with my Gigabyte 4850. It has happened in all the games I've played since I got it (Indigo Prophecy, Crysis and DMC4). The game would start, then anytime between the opening movie's and the beginning of the game(generally if I lowered the settings it would go for longer). I would get one of two errors both from the monitor. Either saying "Digital Signal Lost" then going into stand by, or saying "Frequency out of range" with some random frequencies under it. Which then require a push of the reset button. I managed to mostly fix this by underclocking the memory to 900mhz and doing the XML fan fix.

But here are my problems. First, I have to underclock the memory so I don't get as great peformance. Second I still get the occasional crash. So anyone have any idea what might be causing this? or does it mean its a defective card?

Tried CCC 8.7 (I've used .8 and .9) and got the crash on the 4th loop on the gpu crysis benchmark tool thingy (at 1440 x 900, High settings, dx9). So it would seem that its not the drivers. I'm thinking that it might possibly have something to do with my crap motherboard that won't post if I OC any components even slightly.

It's definitely not the games. I've installed them onto a external hard drive and tried them on another computer. They work fine.

i've same issue too..i tried catalyst 8.8, 8.9 ,8.10 nothing changes..my hd4850 has overclocked fan called IceQ4,my gpu temp is at idle:52~58 on games max 72celcius..how can I fix that problem?i've some errors as pheonix

sigh, I wrote this big long letter and my internet died and I lost it.
summary:
Is your pc overclocked? if it is lock your pci bus at 100 hz. I had the same problem when I was overclocking because I forgot to do this.

Second, post your system specs.

third, how long has it been doing this?

My PC is all at normal clock speeds and the PCI bus is at 100 hz. My specs are: "Asus P5N-SLI" Mobo, "Intel E8400 Core 2 Duo" CPU, 1 x "Corsair DDR2 2GB PC-5300/667 Value Select Ram" (this was probably a bad idea in retrospect) a "Gigabyte R485-512H-B RADEON HD4850" video card and a "550 watt Sun Orb" power supply (I't came with the case). And its been doing this ever since I got it four months ago . Sorry about taking so long I gave up on this thread a while ago, great to see that there are helpful people out there.

I couldn't even find that PSU when I googled it..

Do you know the specs on your PSU?

OK just figured out its a Sun Pro not a Sun Orb (The label was upside down) I cant seem to find the model on the net but here's picture of it with some voltage info on it. I tried blowing a fan into the computer but without much luck. I also did some more tests at default settings (CCC 8.10 seems too let crysis run for a while like this). With fan speed at 40% I got about a minute and a half before it crashed, but on 80% fan speed I got 24 minutes so I'm starting too lean towards the card being crap, but then again I dont know much about PSU. Also please forgive the nonsensical structure of my posts.

Here's the voltages and some other stuff from the side of the PSU.

ATX-550W
ATX SWITCHING POWER SUPPLY

The voltages

RED: +5v @ 38A
ORANGE: +3.3v @ 28A
YELLOW: +12v @ 17A
BLUE: -12v @ 0.8A
PURPLE: +5VSB @ 2A
WHITE: -5v @ 0.5A

GRAY: POWER OK
BLACK: GND

If I do need a new PSU what specs should I look for, I live in Australia so it can be hard to get specific models.

Quick note:

Just because it has a high wattage doesn't mean that it is powerful enough. Remember to check the Amperage on the +12V rails. There are a bunch of Australians on Tom's so just ask!

Gotta go bye!

HUZZAH! Got an "Antec TruePower Trio 650 watt" and things seem too be going great! I'm getting Far Cry 2 soon so that should be a good testing ground for long play sessions.

And actually Crysis would probably be a better testing ground since it is so demanding.

Bloody hell. Well I ran the benchmarker for about 20 mins and it crashed. I think I'm going to take my computer to a shop and have them diagnose the problem. Then ship the dead parts back too the online store I bought them from.

What do you mean a separate power board? You mean like a different power strip?

Oh... So you might have been overloading your power strip?

Yeah... you needed a better PSU anyway..

It might be automatically activating the OC profile, so i'd try deleting the OCing profiles and then set it to defaults. Also what drivers are you using?

This is the same problem on my pc some of the games i have played crashes like tomb raider underworld, call of duty 4, i already reinstalled the drivers updated everything it seems for me its not working fine on windows xp and also the direct x 9c always have some errors on the 3d thingy when i test run it. So i decided to format my drive and install windows vista with direct x10 and now my games works fine no crashes i dont now if this fix the issue but it works for me.