My 2001 windows xp and HP computer has been giving me a lot of trouble.  Will not shut down lately without usinng off/on button and runs very much slower that when I first got it. Do disc clean-up and defragmenter regularly. been to HP support and microsoft support.  they have been of little help.  Have a 2001 HP media center with a pentium 3.2Ghz and am using less than a quarter of 200GB hard drive.  I ask them about reformatting and reinstalling but they keep running me through their canned and ineffective trouble shooting. Any pros and cons on formatting/reinstalling or other options? Asked about new hard drive but was told would not find one compatible with 32. because of inability to cope with the much larger HD memory.  Wondered if new HD could be formatted and sectored into two HDs prior to installation.

Formatting/Reinstalling
Pros - it will work to fix your problem.  If software is causing the problem, when you reinstall the problem software, your problem will resurface.  If you reinstall the software over many days, you may be able to figure out which software is causing the problem.
Cons - it is a lot of work and risky.  It can be a headache if you don't know what you are doing.  Things do not always go back on as easily as you think they will.  If you have valuable data on your harddrive, you risk losing it.

   I don't know what you meant when you said, "would not find one compatible with 32".  What do you mean by 32?  Do you mean FAT32?  Do you mean a 32-bit BIOS?
   Partitioning a harddrive will only help if the limiting factor is the file system (FAT32 is usually limited to around 30gb but NTFS limits are higher than you will reach) or your version of Windows.  If the limiting factor is the BIOS, partitioning is not going to help.  You will need to update your BIOS.

In addition to  clean-up and defragmenting. I would recommend cleaning up the registry,  using RegVac, for instance, and running programs that will search out and remove viruses and spyware.  My experience has been that some of the the biggest problems are caused by registry errors.  In the future, use WinRescue to store versions of the registry that are working correctly, so you can go back to earlier versions of the registry when problems occur.   WinRescue has saved my computers many times.  Don't rely on the Windows Restore feature to get to an earlier version of your system.  It will fail you just when you need it the most.    

Steve Gibson, at grc.com, has a free program, wizmo, which includes a number of options, including reboot and shutdown. The URL is http://www.grc.com. On the site, go to the  free stuff, where you will find a number of useful programs.