Slow laptop

We have a dell inspiron 8500 with xp home edition, 2.2Ghz pentium 4, 512 mb ram. Recently it has been very slow to boot up and shut down. We used to just let it hibernate when the lid was closed but it now takes upto 5 minutes to go into hibernation. I have done error check, defrag, cleared caches, run anti-virus and spyware. Anything elas I could try?

Are you familiar with the hijackthis program? Download it, run it and see what's running on your pc. If you're not sure what you're looking at, save the log and paste in into this thread and we'll have a look.
Have you tried a system restore to when it was running ok?