harddrive keeps spinning

It sounds like the computer is in some form of hibernating or standby. Are you sure it's the hard drive that's spinning and not a fan?
I would look into you power management settings, START>CONTROL PANEL>POWER MANAGEMENT

The first thing I would try if OzMedia's suggestion does not fix the problem, is to verify power management settings in BIOS setup.

Then, swap in a different power supply.

It really sounds to me that all of the power supply voltages are not shutting off when the motherboard tells the PC to turn off.

Alternately, you could have a "normal" Windows shut-down problem, and your motherboard is not getting a proper reset signal.

Check out the Windows Shut down trouble-shooting guide postedat www.aumha.org

Chas

All the above is good, but check your BIOS settings and capabilities. Some systems need to ahve the BIOS set to allow a software shutdown. Some systems do not have the capability for a software shutdwon and require a hardware shutdown as the BIOS istoo old to have the proper power management commands. Sometimes a BIOS update can fix this, sometime it wont.