try going in to start up and cut back on everything that you dont need to have running when you start your computerwhen you re formated that probly got f up
A few months ago when I had my shuttle xpc a similar issue arised. Just like you, I reformatted my hd and reinstalled winxp pro. Then I noticed that the install took way too long. Once it finished, boot time also took way too long(2min).
Turned out to be a bad hard drive(3yrs old). Once replaced, everything was back to normal