Windows XP not restarting

Ok I have a clients computer in for repair and everything is fine except for the fact that when you try to do a restart from within Windows XP Pro it just goes to the “Windows is Shuting Down” splash screen and hangs. If you just chose shutdown it works perfectly. If you hit the reset button it starts up OK so it would suggest that Windows is closing down properly but can’t get to the last stage where it restarts the computer. The Specs are 1.7 MHZ Celeron on a Soltek SL-85SD-C M’Board 512 MB SDRAM with WD HDD and NVidia GeForce 4 MX 440 chipset AGP Video Card. This computer is fully patched and has the lattest BIOS flashed. ANyone got any ideas?