Windows won't start!

Clarifications

Windows Installation won't necessarily correct a corrupt user profile.

Try logging in as THE Administrator when going into Safe Mode. While there, create a new user. Reboot and try logging in as the new user you just created.

If that works, you can reboot to safe mode and log in as THE Administrator again and copy all documents from the old user account to the new user account. If you need help doing that, let us know.

I would use the windows XP CD, insert it and let it run, it will then bring you to a screen with options, you want to choose to go to the recovery console.

In the recovery console you will pick the drive letter with windows on it usually 1:C:\windows

then you can perform a couple of checks, such as chkdsk /f, this will locate any bad sectors in your hard drive and attempt to fix them. Run that and then try to reboot your system and see what happens.

Post back and let me know how it goes.
Good Luck

Repair Install
If XP is corrupted to the point where none of the previous solutions get it to boot,
you can do a Repair Install that might work as well as keep the current settings.
Make sure you have your valid WindowsXP key.
The whole process takes about half an hour depending on your computer
If you are being prompted for the administrator's password, you need to choose the 2nd repair option, not the first.
1.Insert and boot from your WindowsXP CD
2.At the second R=Repair option, press the R key
3.This will start the repair
4.Press F8 for I Agree at the Licensing Agreement
5.Press R when the directory where WindowsXP is installed is shown. Typically this is C:\WINDOWS
6.It will then check the C: drive and start copying files
7.It will automatically reboot when needed. Keep the CD in the drive.
8.You will then see the graphic part of the repair that is like during a normal install of XP (Collecting Information, Dynamic Update, Preparing Installation, Installing Windows, Finalizing Installation)
9.When prompted, click on the Next button
10.When prompted, enter your XP key
11.Normally you will want to keep the same Workgroup or Domain name
12.The computer will reboot
13.Then you will have the same screens as a normal XP Install
14.Activate if you want (usually a good idea)
15.Register if you want (but not necessary)
16.Finish
17.At this point you should be able to log in with any existing accounts.

Please post back if you have any more problems or questions.
If this information is useful, please mark as helpful. Thanks.

boot in Safe Mode, click "my Computer", right click C\:, go to properties, then "tools", Click Error-checking "check now" click both options, click yes, and reboot. This will run CHKDSK, it goes through your OS and looks for errors, tries to fix them, and other stuff... there are 5 stages and the first 4 are fast but the 5th usually takes the longest. Give this a shot, it should help.... post back up if you have any more questions.