Help Required - Computer Doesn't Stay On

[El Xando]

Earlier today, I was on my computer and it was running fine.
Suddenly, for no reason, it powered down. Just straight off. It then started again about 2 seconds later, so I went downstairs to see whether it had been a power cut. There hadn't, and when I went back up it was on the Desktop. However, shortly after it did the same thing again.
It now turns on and either tries to enter the bios and crashes very shortly after, or turns on, and stays on but nothing happened - the monitor registers no input.
We took it apart, cleaned it with a can of compressed air and have tried it with floppy drive disconnected, DVD drive disconnected, RAM disconnected, to no avail.
We put a multimeter on one of the power outlets from the power supply, and it goes down as the computer goes off, then comes back up when it restarts.
What is going on?
Thanks for any help.

 

[Dan]

This is a bit of a wild guess, but might it have been due to an overheat? My computer kept turning itself off yesterday too.

 

[El Xando]

This is a bit of a wild guess, but might it have been due to an overheat? My computer kept turning itself off yesterday too.

Thanks for the suggestion, but we're pretty confident it wasn't as all the fans were running fine, and it didn't seem hot, and was also left for quite a while before being turned on at one point and it just went straight off again.

Any other ideas?

 

[Andy]

Have you tried using another HDD?

 

[El Xando]

Well we tried it with both HDDs unplugged through both power and connection to motherboard but it still couldn't stay on...

 

[Dan]

Have you installed an anti-virus or a firewall or anything? I installed a version of Kaspersky the other week and that kept making my computer reboot. Try booting into Safe Mode and run a System Restrore to a couple of days back.

 

[El Xando]

Have you installed an anti-virus or a firewall or anything? I installed a version of Kaspersky the other week and that kept making my computer reboot. Try booting into Safe Mode and run a System Restrore to a couple of days back.

I had AVG Free Edition, but I haven't installed anything new recently and it rarely boots past the bios so I can't even try to get into safe mode.

 

[Bill]

It's probably the motherboard or the CPU. I had a simillar problem about 2 years ago. It would start to boot up, but would never get passed the splash screen. Replaced the motherboard and CPU and all was good.

 

[ilyace]

Tbh It sounds like cpu overheating. You said all of the fans were running fine, does this include the cpu heatsink/fan? When the computer is on do you have time to download some kind of temp monitor program so we can make sure? If you can, I suggest CoreTemp or something like that and just post your results here.

 

[Cryox]

Tbh It sounds like cpu overheating. You said all of the fans were running fine, does this include the cpu heatsink/fan? When the computer is on do you have time to download some kind of temp monitor program so we can make sure? If you can, I suggest CoreTemp or something like that and just post your results here.

You should read the entire thread before posting. There aren't that many posts to read.

I had AVG Free Edition, but I haven't installed anything new recently and it rarely boots past the bios so I can't even try to get into safe mode.

 

[ilyace]

You should read the entire thread before posting. There aren't that many posts to read.

..You're cool.

Regardless, it sounds like a heating problem. If it's not that than your cpu/mobo/ram could be faulty.

 

[Sousanator]

I sorta have the same problem with my PC right now. It doesn't shut down unexpectedly, but I always have problems starting it up.

I have to fiddle with the power switches about 20 times before I can actually get to the bios screen. But unlike your problem, once I get to the bios my PC will stay on correctly

 

[El Xando]

It's probably the motherboard or the CPU. I had a simillar problem about 2 years ago. It would start to boot up, but would never get passed the splash screen. Replaced the motherboard and CPU and all was good.

It would be a real pain if it was the motherboard or CPU
We're going to see if it's the PSU first and after that we will look into those two.

..You're cool.

Regardless, it sounds like a heating problem. If it's not that than your cpu/mobo/ram could be faulty.

I'm pretty confident it isn't a heating problem because it has been left for a day and tried again to no difference. It literally can't stay on for a second before it goes off now...

 

[DrLame]

<deleted due to content>

 

[Mraellis]

Its either your PSU or MB. Try a new PSU in it, there not much to buy.

 

[El Xando]

A new motherboard later, we believe we have figured out the problem.
My graphics card requires a 8-pin PCI-E connector for extra power. Since my PSU lacks one, we had been using a 6-pin to 8-pin PCI-E adaptor. However, 6-pin cables only provide 75W as opposed to the requires 150W. So after some time, the PSU couldn't supply the graphics card the correct amount through the 75W cable anymore.
So what we are going to do is use the 6-pin cable and a 2 molex to 6-pin cable with a Dual 6-pin to single 8-pin PCI-E adaptor. The only thing is, we can't find a Dual 6-pin PCI-E to single 8-pin PCI-E cable anywhere.
If anyone can find one of these in the UK, it would be GREATLY appreciated.

 

[Hardrive]

I sorta have the same problem with my PC right now. It doesn't shut down unexpectedly, but I always have problems starting it up.

I have to fiddle with the power switches about 20 times before I can actually get to the bios screen. But unlike your problem, once I get to the bios my PC will stay on correctly

The same thing happened to me just last week. What I wound up doing was replugging EVERYTHING except the processor. Then it booted just fine.

 

[MenaceInc]

A new motherboard later, we believe we have figured out the problem.
My graphics card requires a 8-pin PCI-E connector for extra power. Since my PSU lacks one, we had been using a 6-pin to 8-pin PCI-E adaptor. However, 6-pin cables only provide 75W as opposed to the requires 150W. So after some time, the PSU couldn't supply the graphics card the correct amount through the 75W cable anymore.
So what we are going to do is use the 6-pin cable and a 2 molex to 6-pin cable with a Dual 6-pin to single 8-pin PCI-E adaptor. The only thing is, we can't find a Dual 6-pin PCI-E to single 8-pin PCI-E cable anywhere.
If anyone can find one of these in the UK, it would be GREATLY appreciated.

I wouldn't recommend this idea AT ALL.
It'd be a much better idea to get a new PSU.

Ninja Edit: New PSU suggested as well