Hi,
Perhaps before reinstalling Windows XP you can try doing a repair
installation which would perserve your files/settings, but fix any damaged
system files etc.
Follow these steps to do a repair install.
1. Insert the Windows XP CD into your computer's CD-ROM drive or DVD-ROM
drive.
2. Restart your computer. If you have to, change the BIOS settings to start
from
the CD-ROM drive or DVD-ROM drive, and then restart your computer again.
3. At the "Welcome to Setup" page, press ENTER.
4. Press F8 to accept the Licensing Agreement.
5. Use the arrow keys to select the installation of Windows XP that you want
to
repair, and then press R to start the automatic repair process.
6. When Setup is completed, activate Windows XP.
Note that you will need your Product Key for this procedure, so have it
handy before you begin.
How to Perform a Windows XP Repair Install
http://michaelstevenstech.com/XPrepairinstall.htm
If after doing the repair installation of Windows XP and you're still
experiencing the same restarting issues, then your best bet is to properly
start off clean and install a fresh copy of Windows XP and wipe everything
on the partition out.
Easiest way is to take your Windows XP Installation CD, and boot your
computer off of the CD. You may have to go into your BIOS to tell your
computer to boot off your
cdrom.
Once it starts booting off the cd, this will startup the Windows XP
installation process.
During the process, it'll ask you where you want to install your Windows and
options are given if you want to delete the partition and format the hard
drive.
Choose the format hard drive option and continue the setup and you'll have a
fresh brand new install of Windows XP.
Remember when choosing the format hard drive option all your data on that
hard drive or partition will be lost.