did you check you Pc for spyware, viruses?
You can also try this:
start-->RUN and type msconfig and hit ok.
on the window click on the start up TAB, uncheck the ist and then hit apply and then ok. it will ask you to reboot and then try one more item.
if that doesn't work. You can also try this.
start-->run and type sfc /scannow. You will need the winXP for that.