Computer trouble, help quickly please!

Our computer (5 years old, cheap, Windows XP) has started turning itself on and off... and on, then off... etc.

I've done the stuff I can do... cleaned it, checked that it's all plugged in.

Any ideas about what may be happening?  Hopefully it'll keep working long enough for me to see any suggestions!  If not, thanks in advance... and see you when I've bought a new machine.

Our old computer kept turning itself off...the problem?..it was getting overheated.

-How often does your computer stay on?
-Take off the side case on the computer and look inside,is there a lot of dust..especially around the fan?

If neither of those seem to be it...then it sounds like its time to get a new computer. Usually around 5 years they seem not to want to work anymore!

Still here, for now...

Cleaned the insides on Friday, esp. the fan.  (It wasn't very dusty, which is weird.)  I've got someone coming over to look at it later today or tomorrow... a someone who actually knows about computers, so hopefully it can be fixed.

The problem isn't consistent.  Today I've only had two incidents, so far.  Last week, one day it couldn't be used at all, the next it was fine... If this is a loose connection somewhere, it's going to be tough to pinpoint.

Time to start making backups while it's still working...

Make your backups and start looking for a new one.

Madeira we had the same problem. We backed everything up on cd roms and got the hard drive cleaned but a couple of months later it just went again so we have bought a new one.  Be careful with your internet usage in the meantime, I think it was a file sharing thing that killed ours in the end. 

Has the computer been scanned for viruses or malware?  The only time I've had a computer behave like that was when I had a virus. I had to reformat and reload everything.

Usually when that happens it's a graphics card problem. Not sure if yours is on board or in a pci slot, but it's not a good sign either way. Make sure you back everything up because regardless, you'll either lose everything from the motherboard blowing or just need a reformat which you'll still lose things. Hopefully it gets sorted for you

A poltergeist maybe? 
just kidding!   

Hard to tell without some more details and having a chance to "poke around" inside the unit.

When you say it just switches on and off randomly, does the switch off go through the full shut-down routine or does it just go off instantly, just like you'd pulled the plug?

It goes through a full shutdown.  (If it was like pulling the plug, I'd assume it was my foot hitting the transformer toggles... which happens sometimes.)

Off-topic, probably, but I did try to use the computer without a transformer when we first arrived.  There's a switch on the back to change to UK power.  It didn't work, though... there was a burning smell and then an alarm went off in the machine.  It's been fine for a year now, though.

I thought it could be a virus, but neither spybot SD nor AVG can find anything serious.  ZoneAlarm is running fine... are there other (free) programs I should try?

The computer guy has yet to show up... he was talking about installing a new OS.  Does that make sense to you guys?  (It WOULD be nice to have an English OS, though..)

Still working today, so far!

It goes through a full shutdown.  (If it was like pulling the plug, I'd assume it was my foot hitting the transformer toggles... which happens sometimes.)

Off-topic, probably, but I did try to use the computer without a transformer when we first arrived.  There's a switch on the back to change to UK power.  It didn't work, though... there was a burning smell and then an alarm went off in the machine.  It's been fine for a year now, though.

I thought it could be a virus, but neither spybot SD nor AVG can find anything serious.  ZoneAlarm is running fine... are there other (free) programs I should try?

The computer guy has yet to show up... he was talking about installing a new OS.  Does that make sense to you guys?  (It WOULD be nice to have an English OS, though..)

Still working today, so far!

OS - is operating system so ya if your computer keeps shutting off then installing it could solve your problem

Sorry, I know what OS means... I just happen to think I have an electrical problem.  Not sure how a new OS would help.

But I am a computer dingbat.

my apologizes, I read it as , it sounded like you were asking what OP meant

Basically an OP runs everything in your computer. Its the most important program that runs on a computer. Every general-purpose computer must have an operating system to run other programs. Operating systems perform basic tasks, such as recognizing input from the keyboard, sending output to the display screen, keeping track of files and directories on the disk, and controlling peripheral devices such as disk drives and printers.

So if its turning itself on/off then its more then likely to be a fault with an OP. Since you've said its not overheated and etc.
It doesnt sound to me like its an electrical fault. When our computer acted up like yours I re-plugged it in every socket in the house and it still did the same thing. We just ended up buying a new one because after awhile it couldn't be bothered to turn on anymore!... It was a sad sad day...

It could be a software problem, but it could be something as simple as a faulty switch if your system is configured so that pressing the power switch initiates the shut-down sequence.

Off-topic, probably, but I did try to use the computer without a transformer when we first arrived.  There's a switch on the back to change to UK power.  It didn't work, though... there was a burning smell and then an alarm went off in the machine.

Hmmm.... That's not good.   Are you sure you had it set to 240 before connecting to the U.K. outlet?   

A faulty power supply could also initiate a shut-down on some systems.  Obviously if it just lost all power it be gone in an instant, but on some supplies there's a power quality signal which tells the system to close down. 

Not 240... I think the switch says 230.  (It's dark now..)  I certainly changed the switch, though.  And changed it back right pronto.

Today I did a registry clean.  Not sure if that's going to help, but someone suggested it... and it's the first time I've heard of such a thing.

Still waiting on the computer guy.  No problems at all today, though.