My computer restarts when playing games?

I have recently re-applied thermal paste on my CPU and HD Radeon 4670 card 1 GB ddr3.

They don't overheat as i have checked the Temps through hardware monitor form CPUID as well as speed fan.

I am guessing that the problem is with the PSU. I have a 450 Watt PSU which ran fine for a year but now my comp is restarting while playing games.
HD 4670 card recommends 400 Watt PSU.

i reached this conclusion as i have removed automatically restart computer if error is encountered in startup and recovery and i dont get any blue screens or green screens as the computer restarts...nor any error messages.

Further details: Core 2 duo 2.2 Ghz E4500, 2 GB DDR2 ram with intel D945GCNL MOTHERBOARD and Windows 7 Ultimate 32 BIT operating system.

Computer is 4 years old.

Graphic card and PSU are 1 year old.

Thank you for your time...

The 450w PSU should be more than enough for your system. Do you happen to overclock?

Thanks for the quick reply.

I haven't overclocked my Graphic card. It is left at factory settings. Also My PSU is Mercury 450watt 20+4 pin.

I am aware that 450 Watt is enough for the computer but is there any problem with the connections or power supply with the PSU wires like wear and tear problem though i couldn't find any visible damage to the wires. Also it ran properly till 1 year.

Random is right in that a quality 450W PSU should easily power your system. Mercury PSUs aren't known for their quality/reliability.

Did you change settings in order to stop auto reboot on failure/error? If not, then you may be getting a BSOD without knowing it. Can you check your log files to see if you're getting any errors in there. If you're really not getting any error reports, then I would lean towards a faulty PSU.

if you mean in windows event viewer/log

I have some DNS and DHCP error...but those are due to internet connectivity...those are okay..

But i have a kernel-power critical error...it says as follows...

//The system has rebooted without cleanly shutting down first. This error could be caused if the system stopped responding, crashed, or lost power unexpectedly.

event ID: 41

PSU's get worse with age, a poor quality PSU will a) get worse quicker and b) start off worse. So yes a PSU can just stop working after a year, in fact they are more likely to stop working after a year.

http://support.microsoft.com/kb/2028504

windows shut down unexpectedly, which is exactly what you'd see from an underpowered psu being stressed by an upgraded GPU.

If you put it in another machine, there are 2 things that will happen
either:
nothing will happen as the other machine requires less power.
or:
the other machine requires more power and it will fail, possibly damaging the other machine (a recent patient of mine lost a Mobo like this)

that is the collective wisdom so far

I found the solution.

It was those stupid Windows Updates...For a year i hadn't updated Windows so there was no problem. So i re-installed Windows 7 and turned off automatic updates. Now I haven't gotten and reboots or errors in log while playing Arkham Asylum for 4 hours and everything is working perfectly. I hope it stays like this for atleast a week to confirm that this is the solution.

thanks for all your help Rugger and also thank you 13thmonkey. i am so happy now yeaaaaaaa!!!!!!!!

You're welcome and good luck with system stability...let us know if you have any more issues.

Well I know no-one else with this problem, it indicates other problems. Possibly a memory error. Can you run memcheck from your win7 disk?