Computer Problem

My computer shuts off during the startup phase, before Windows fully loads.
I turn it on, the fans start running, and less than five seconds later the thing turns itself off.

I usually have to go through the process 5 or 6 times before it finally boots up properly so that I can use it.
It's a new computer and I am running Windows XP.

Any help would be appreciated.

Do you see anything on the screen before it turns off? ie, do you see a memory check, listing of what hard drives/CD ROMs you have etc.
Does it even get to the Windows XP splash screen?

It boots normally (shows the drives, cpu, memory, etc.) and will occasionally get to the XP splash screen, but sometimes not.

Might be a power supply problem.
Do you have another PS you could stick in it to test with?
Alternatively, it might be the circuit in your house. A friend of mine once had the problem that if a light switch was turned on, his computer would reset/turn off because of a temporary surge in the circuit.

You might have a Virus that is making it do that as well. I had one awhile back that did that.

Have you added anything to your system within the last couple of weeks? I would check that power supply first.

-First, check to make sure you have the proper region switched on your power supply. If you live in North America make sure it's on 115. You would be surprised how many PCs I've seen set incorrect and customers were complaining of "something's wrong with my 'puter"
-Then check the AC wall outlet by seeing if you get intermittent problems on another outlet.
-If not, then check the wattage of your power supply. How much wattage does your powersupply produces? Check the model number, because any info on the label otherwise will lie to you.
-This day and age if you have a power supply over 300 watts then you should be fine. Otherwise, I think it's your power supply. What is on your machine? I.e., video card, cd/dvd rom drives, hard drives?