what could it be?

Got following computer

gigabyte 990xa-ud3 motherboard

AMD 6300fx processor

8gb corsair ddr3 1600mhz

saphire 7950hd (the factory clocked version)

samsung hard disk

ocz ssd

now its not shutting shutdown where you would expect - like using hardware intensive games, its just very occasionally, like once every few days, usually when doing something like web browsing.

Ive flashed my bios to latest version (last week when i installed new processor)

Temperatures are as follows following a shutdown 

7950 is at 37 celcius

processor is at 28 celsius

which are very safe temperatures

ssd is24 celsius

hd is 32 celsius

theres some temperatures on the boards which reach 32, 35 and 41

im thinking is dodgy latest bios flash??  maybe go to older version? not sure?

oh should add fitted aftermarket air cooler to the processor (had one from old processor that i overclocked but im not clocking this one)  and ive put my own silver paste on and stuff.

forgot power supply its a corsair vx550w.  Im pulling 330w at peak times.

Usually that's a motherboard related problem - could be BIOS, could be driver-related, could be power supply flaking out (or has already flaked out and is starting to damage other parts).

But those kind of glitches are hard to track down, and none of those parts are smoking guns by reputation anyway.

One thing to check: when you were in doing brain surgery and changing out the heat sink: make sure all the cards are seated well - make sure no heat sink compound dripped/squished over the side of the CPU and got into the socket. Make sure all the cables are seated well (it's very very easy to loosen a power cable or something). Make very sure there are no stray pieces (cables/screws/zipties/etc) hanging out inside the case.

From my personal experience, it's the motherboard.  i had a computer do this for about 6 months, it would only happen like every couple of weeks, and it would also freeze upon starting windows xp sometimes also.  Oneday I went to turn it on and the fans came on, but that was all. /sadpandaface

Edit: I opened it up and the motherboard had a big black burnt mark across it :(

Originally posted by ShakyMo
Sudden outage like when a processor overheats. But I've got a temperature monitor and cpu is running in the 20s which is perfectly fine.

Now I've switched to Chrome instead of FireFox it appears to be ok, but its weird and I would like to get to the bottom of it.

Its actually likely an issue with Firefox and your version of flash believe it or not. This has been a common issue as of late. Search the firefox forums and you will see a number of others sharing a similar issue while using firefox and firefox only. I my self actually had the same issue. 

Check and make sure your version of flash is current, if so uninstall firefox and reinstall it. This fixed it for me, though after that I rarely use firefox. Not a fan after the issue and after seeing how many shared a similar issue. 

Originally posted by GrayGhost79

Originally posted by ShakyMo
Sudden outage like when a processor overheats. But I've got a temperature monitor and cpu is running in the 20s which is perfectly fine.

Now I've switched to Chrome instead of FireFox it appears to be ok, but its weird and I would like to get to the bottom of it.

Its actually likely an issue with Firefox and your version of flash believe it or not. This has been a common issue as of late. Search the firefox forums and you will see a number of others sharing a similar issue while using firefox and firefox only. I my self actually had the same issue. 

Check and make sure your version of flash is current, if so uninstall firefox and reinstall it. This fixed it for me, though after that I rarely use firefox. Not a fan after the issue and after seeing how many shared a similar issue. 

This ^   ^

you know fingers crossed it hasnt happened since i switched to chrome

its a weird bug as i said, Ive been having 6 hour planetside 2 / hd modded skyrim sessions and not had any problems.

had a little poke about in the case too,  one of my 12v GPU rails was across the CPU fan which wouldnt have helped with airflow, but then my temps were fine anyway.