my PC was WORKING fine yesterday , today it powers on for seconds and then powers off again , what could it be ? it's a pentium D 3.4 GHz , 2 GB RAMIs this a desktop over 3 years old?
Is it running Windows XP? Vista? Any error messages?

Most likely hardware issue is a fan has stopped working. The will stop a PC is less that a couple of minuets.
yes it's 6 years old ... running windows XP , doesnt wait  to boot into windows ... the processor fan and the case fans both work Sounds like the power supplyi removed the processor fan and found the processor very hot , is it normal or there's a problem with the COOLING ?

Also if it's a power supply , it WONT power on in the first place right ?Power supplies don't always just die - they often start to go bad with different symptoms - including the one you're describing.ok thanks ... is there anything i can do to make sure or i am LEFT with buying a new PS option Just make sure you GET it from a retailer who will take it back if you don't need it.Many Thanks AllanTwo more things to check.

1. A failing floppy drive or a failing CD-drive could also cause the symptoms.

2. Judging by your comments, the CPU may have lost intimacy with the heat sink. Check and see if the heat compound has dried up or  caked. In six years it  could happen.

thanks geek , so i will try cleaning the heat sink and applying new thermal paste if that's what u mean Quote from: superdupermido on January 01, 2013, 02:17:49 PM

thanks geek , so i will try cleaning the heat sink and applying new thermal paste if that's what u mean

That's what I mean. Make sure is is seated right. Heat transfer is very important with modern CPUs.