Computer has started to randomly shutdown while gaming

[Nanek]

So the past few weeks my PC has started to just shut down without warning, but it only happens during a game (eg: TF2), seems to run fine if I'm not playing anything. I've checked the temps and they seem okay going by the logs (gpu: 60-70C cpu: 50C), I've never really had this issue until now and I've had the pc since February.

I was thinking it could be the PSU. Once the pc shuts down it wont turn back on unless I switch via the mains, wait 5 minutes, then turn it on. If I turn the mains off and on quickly the fans spin up but then it all powers down in less than 1 second.

Anyone have any other ideas of what it could be?

quick specs:
AMD x2 550 BE
ati 4890
4gb corsair ram
samsung F3 500gb
NorthQ Black Magic Flex 850W PSU (I bet it really is the problem *sigh*)

[Mithrandir]

I would say its PSU as well going by your comments. IT seems the PSU needs to cooldown or be reset before starting up again, but Im sure others will have suggestions of have experience of this situation.

[smargh]

1. Don't trust the temperature readings. Use your fingers.

2. Probably the PSU. Remove it and shine a light into it to look for bulging capacitors. For poor quality capacitors, expect a PSU to last 2.5 to 3 years, then replace it anyway. However, this isn't a rule of thumb: my auntie has a crap Qtec which she's been using fine for 5+ years.

[Pingu2003]

is anything overclocked?

[Nanek]

Everything was at stock when this happened. I've just swapped the psu out with a corsair VX550 from my brothers pc (probably has just about enough power considering the fan is spinning like mad on this), so far so good but I haven't played anything for over 1 hour.

Does anyone reckon it is related to an overheating psu? supposedly the fan is load based instead of temp based, so considering that summer is here maybe it couldn't handle the heat? especially since this VX550 unit is fairly loud when gaming and I'm sure that fan spins up with higher heat levels. I wonder if its worthy of an RMA by scan :|