Another restarting prob

[rover3500]

Hi everyone,
Another random restarting.
It started when my monitor took longer and longer to sync(over months)till it wouldn't sync anymore,but then when i borrowed a monitor it wouldn't go on so i tried on my mrs pc and it worked.Changed to internal graphics on my Mobo and it worked.
Bought a cheap HD5450,put it in,worked ok.For a while.(A day or 2)
Then started restarting randomly,sometimes only once a day,sometimes a few times.
Changed motherboard to last one I had(which is what i have in now)
Put my original Graphics card back in just to see(9600GT) also used a new case(not new PSU tho')
Put decent thermal paste on cpu,Have decent cooler but can't remember make,is a recommended one.Also put paste on GPU.
It still shuts itself off(might not restart due to new Mobo settings)all of a sudden,no reason.
Can play Elder scrolls for hours without it shutting off,can hear gpu fan hacking so is getting hot,hasn't gone above 63 degrees,but idles at 56.Is that normal?
Anyway Pc still shuts off whatever graphics i use(3 different),tried all memory combos in and out(4 x 1 GB sticks,tried 2GB in and 4GB in)different mobo,reinstalled windows 7 x32 twice,tho' it's not a windows or driver thing.
Earlier it shut off,I tried turning on but turned straight off.But waited a half minute and it waited longer b4 it shut off.So waited few mins,came back on.
Have been closely watching the temps,and the Cpu never goes above 43 degrees,even seconds before shutting down,and the Gpu is usually about 56 and it get's higher than that playing games.Mobo temp is usually about 36 degrees(all just before it shuts off).
I'm really stumped now,it seems like a temp thing if waiting longer allows you to turn the pc back on without shutting off,but they seem ok.
Any suggestions really appreciated and sorry long post,just want to tell all info.
Thanx

Sorry thought my signature would come up.
Asus M3N78-EMH HDMI
Phenom x4 9550 2200Mhz
1Tb Samsung f3
9600GT Nvidia
4GB 667 Ram (4x1GB)
500W PSU

 

[jsc]

What kind of PSU?

Have you tried changing the PSU?

 

[rover3500]

It's just a casecom and no i haven't.I have already bought a graphics card that i couldn't really afford,just don't want to get another PSU needlessly.I know they do go funny tho.Another thing I forgot,when i tried to do any of the burn in tests for the cpu on the ultimate boot cd,it came up with a list of stuff and locked up.Not being able to allocate pointers and a kernel danger it said on all.Could still be power supply tho.

 

[rover3500]

Could a hard drive problem do this,I wouldn't have thought pc would turn straight back off of that was the case.Just want to rule things out,then just down to cpu or psu,i think.

 

[rover3500]

Solved.

Was the power supply.
When I took it apart it was half full with fluff and dust from last 5 years.
All the components were caked in it.It went completely in the end so decision to buy another made for me.
Got another with 2 fans so it blows thru(into the pc)but i clean that every few months anyway.

So a suggestion for anyone thats had power supply for ages,is prob worth taking lid off and cleaning out every so often so it doesn't overheat,especially if ur like me and have a dusty house.

Thanx

 

[rover3500]

Best answer selected by rover3500.