Sometimes our windows stop responding on shutdown.It may crash and freeze and stop responding, but it won't shutdown.Below are possible causes of this:


1) Bad device or bad device driver:
These devices can cause problem,Modems, network(LAN) cards, sound cards, graphics card, printer and others.

Solution:
Have you added any new hardware to your system.If yes, remove it.

Remove all external devices connected to your system like thumbdrive/pendrive, mp3 player, printer, modem, TV tunes card..and graphics card(if you have any).


2) Virus problem:
Another cause can be unwantes script installed in your system.

Solution:
**Turn off system restore.
**Install 1 good antivirus and 2 good antispyware.
**Update your antivirus and antispyware.
**Boot in safe mode, and do full system scan with antivirus and antispywares.
**Also, if possible perform online scan. Some are -

www.kaspersky.com/scanforvirus
security.symantec.com/
www.bitdefender.com/scan8/ie.html


3) New Software creating problem:
You have installed any new software.The newly installed software may be creating problem

Solution:
Uninstall all software installed since you started facing this problem.Or restore your windows XP to best known time.This will fix your problem.To restore your computer:
Start-->> All Programs-->> Accessories-->> System Tools-->> System Restore.
System Restore winddows will open.from there select the date of best known configuration.


4)Windows Registry error:
Another cause can be crupt windows registry.

Solution:
Repair your windows registry using some registry software. Download Registry Fix.


5) BIOS problem:
Problem can be in your BIOS.

Solution:
Update your BIOS, and set it to default setting.

The best solution is system restore. If nothing works above all mention solution than it is suggested you to repair your windows XP with no external hardware connected to system.