Well, you can try formating the hard drive, but that will destroy all existing data in the computer.
To do this, create a startup diskette. Go to the Control Panel and select the Add/Remove programs. Select The Startup Disk tab. Insert a new Formated diskette in the floppy drive and click on Create Disk.
Use the Diskette to boot the machine. Select Command prompt with CD Support. A letter will be assigned to the CD_ROM. At the prompt type the following:
Format C: /u
Press Enter. At the completion of Format, insert your installation CD and type the following:
X:SETUP
Where X is the letter assigned to the CD_ROM. Press Enter ans follow instructions on screen
Now, before yo do this, post the error messages you are receiving. We may be able to identify. the source of the problem. When posting back, download Hijackthis and run this program. Post the log here and let us take a look:
http://www.majorgeeks.com/download3155.html
Best wishes!