If it's XP not starting up as your post implies, then pressing F8 during boot up will take you to a screen that has several selections. One of them is> last known good configuration. Select this and see if it boots up.
If it does then click the start button and select > run.
Type in just as you see it and yes there is a space between the c and the /.
Put your XP cd in the drive and hit enter.
If it goes well it will check all the system files and replace any that have been changed or corrupted.
If you can't get to here you can post back and we'll take a look at other options.
But then if the hardware is not turning on then let me know that. It puts a whole different slant on the problem.