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Time on a technician’s bench always costs money, but this is $50 or so you can EASILY save yourself.

1 ) Grab your Windows CD and put it in your CD drive
2 ) Watch your power-on screen for a prompt that says “Boot Menu=F8″ or similar. On most PCs, the boot menu will be F8, F11, or F12
3 ) When the menu pops up, choose your CD drive and hit enter
4 ) Press enter to boot to the disc when asked to
5 ) Once the blue Windows setup screen comes up, press R.
6 ) Wait for the countdown on the next screen to finish.
7 ) Press 1 and hit enter.
8 ) Hit enter again when asked for the Administrator password.
9 ) Now type in: chkdsk /p [enter].
10) When it’s done, type: exit [enter]

This will run a checkdisk in the command prompt and will almost definitely fix your boot problem. There are other causes, of course, but this tip will usually do it!