Shutdown Problems on Windows XP Pro SP3

I have updated to the new SP3 on my PC and everything was OK for a day or so, then I noticed that it started taking a while longer to boot down and turn off than normal. I have checked everything I know to. I have run all my Anti-Spyware and Anti-Malaware and Anti-virus software and even ran Advanced Windows Care and I can’t seem to find anything changed or wrong! It takes about 2 minutes to shut down on its own and it never took over 20 seconds before. Any Ideas?