windows xp won't start up

when I came home my computer was off with no signs of power outage...I started the computer and an error message said, "previous shutdown due to thermal event." and it gave me the option of pushing F1...this brought me to the screen that has the normal start up and or last known good config...when choosing different options, the same thing happened...the start up got to the windows logo page for 1-2 sec and then the computer just shut off...any ideas?

is this a laptop or desktop? check to see if the fan on the heat sink is running and take a can of compressed air and blow the dust off the fins on the heat sink. the problem is most likely the processor is over heating causing it go into thermal shutdown.

It is a desktop...I did clean that area this afternoon, but when I opened up the case the fan on the power suppy??? wasn't turning and when I cleaned it and got it going I was able to get windows to open...but after a while the computer kicked off again...does the power supply need to be replaced or can the fan be replaced...thanks