Hi Juliana,
You will first need to change the boot order in your BIOS. To do so, press F2 as your computer boots up. This will take you into the setup. Poke around for a boot order and make sure the CD drive is at the top, and the HDD is at the bottom. Sorry to be kinda vauge, but terminology varies between BIOSes.
Next, insert the XP CD into the CD Drive and reboot the computer. This should make your computer boot from the CD-ROM. When a blue setup screen appears, press R to repair the installation. This will open a command prompt. From the command prompt, we will run a disk diagnostic and attempt to fix the boot record.
In the command prompt, type in
chkdsk /r and press
Enter. This will check your hard disk for errors. Once that has finished, type in
fixboot c: and press
Enter. This will attempt to fix your Master Boot Record.
Let us know if this works. If it doesn't, don't worry, there are more steps we can take!
Also, what kind of computer do you have?
Good luck!
edit: Thanks Zeus! lol I get this one all the time.... So I know how you feel!
Edited by The Admiral, 27 November 2007 - 07:49 AM.