Startup: Scrolling Bars Stop And Freezes Before Loads Desktop?

recently my computer takes ages to get passed the Windows XP load screen. Sometimes the scrolling bars stop and it freezes before i it loads the desktop. It works if i safe boot it, but often it doesn't pass the Windows XP startup screen, or it takes a long time (approx 100s) to get passed it. Before it only took at most 10 seconds. It don't know why it's doing it. I've tried running a registry mechanic, prefetch cleaner and all that jazz.But it's still taking awhile to get passed that XP screen.