Remove New Hardware and Reboot
Step 1
 
Turn off the computer and open the computer case.
Step 2
 
Remove the new piece of hardware from the computer.
Step 3
 
Restart the computer. If Windows XP restarts successfully, then the issue resides with the new hardware or its software driver.
Reboot in Safe Mode and Remove Third-Party Applications
Step 1
 
Turn off the computer. Wait 30 seconds and then restart the computer. Press the "F8" key after the boot screen and until the Windows Advanced Options menu appears.
Step 2
 
Log in to Windows XP using an administrator account. Click on "Start” and "Control Panel."
Step 3
 
Double-click "Add or Remove Programs." Select the software product from "Currently installed programs" list and click on "Change/Remove." Follow the onscreen instructions to remove the program.
Step 4
 
Shut down and restart Windows XP normally. If Windows XP restarts successfully, then the issue resides with the software.