I have a dell inspiron 5100 w/ win xp. When I power it on it will go to the windows start up screen but after that goes away it shuts off. After that it will power up but will turn right back off. Doesn't even make it to the windows start up screen. I haven't made any changes to the computer... any ideas on what it could be?

Initially, check all air flow openings for dust build up and clean if required.

If air vents are clean, try booting the laptop with a bootable media to see if the symptom persists. If it does, the problem is most likely hardware related as opposed to O/S related.

Post back with your results.