Software

The computer will not turn on or the OS will not load?

If it's the OS 7 has the option to Rebuild the OS if you made a Recovery Disc as per the instructions.

If however you mean the computer will not turn on that's a bit more difficult.

Col

1) Take out the battery and just plug in the adaptor.
If it works then your battery is either flat and needs a recharge or it is dead meaning you need a new battery replacement.

2) If any lights come on and then go off it could be a heating problem or the harddrive needs a look at or a replacement.
Have a look around the laptop for any dust around the air intakes give it a good clear out.
If it is all a no-go then a trip to the repair shop is a good choice.
Hope all works out for you.

there is not much information, so it is difficult to make useful suggestions.

First, make sure the computer is shut down completely. Unplug the power supply and remove the battery. Let it sit idle for an hour or so.

Then reconnect power, attempt to boot, and during boot hit the "F8" function key and start Windows in Safe Mode. After it is running, shut down and try to restart normally.

If that does not work, give more details what happens when you try to restart.