My PC has been turning on and off by itself does anyone know what i need to do to fix this

call an exorcist....

DEEP virus scan....sounds like a virus big time...might even have to take it in to get that one fixed...

right click on ur desktop go to ur screen saver then to power make sure that all the power says never to shut off an that should help it could be in a sleep mode

Or a lose cable. And anytime your foot or leg nudges it or a pet walks around it, it goes out. Sometimes the problem is a simple one. OR the exorcism might not be a bad idea.

You might want to check the power supply, mine done that and the power supply had to be replaced.

as okie said,deffinately check the power supply.mine started doing that not too long after i bought it and it did it for a year until the power supply finally blew.

if it's the power supply,change it before it takes the motherboard with it

either virus or cable supply...mine did that...then just as I was to transfer the recent stuff I hadn't gotten on cd yet it didn't turn on ever again...so LOL...I used my warranty and got a new Toshiba. :-D

thank you everyone

Check your power options, to see if your computer is allowed to shut down / start up on it's own.

If you have installed any new hardware to your computer, remove it to see if that fixes the issue.

Do you have an electric heater near your computer? If so, it could drain the circuit enough to shut your computer down. Move the heater (if one exists) to another circuit or leave it off and see if that corrects the problem.

Check the power cable, make sure it's plugged in correctly.

If your computer is connected to a power strip, check that. If you have a spare, replace it just incase.

Download http://www.almico.com/speedfan.php to monitor your computer's temperature. It could be that your heatsink isn't working properly, which would be a simple fix.

Reseat your RAM and CPU, by taking them out gently and then putting them back in.

Defrag / Error-Check your HDD.

After this, it becomes more complicated. You will have to replace hardware and you will be guessing at best. It could be anything from Powersupply to RAM to HDD.

Good luck