My Fujitsu Laptop running Xp w/SP2 will not start up

I have been having a few issues lately with my laptop just shutting down all of a sudden. I finally figured out that it was over heating due to blocked air vents on the bottom. Prob, fixed.
Well, apparently not.
I restarted and it is now just going around and around in the start up boot phase.
Starts to load, gets to Windows is starting up..for about 10 seconds and then it goes right back and tries to restart again getting to Windows is Starting up …around and around.
What do I do now???
HELP!!!
I have tried booting up in all sorts of different modes including Safe mode but same thing with all of them.