You may have too many programs trying to start at the time of start-up. Have you tried to wait long enough to see if it would finally start? If it does, I would recommend downloading bootvis from microsoft that actually helps speed up boot times, worked for me.
http://www.microsoft.com/hwdev/platf...ot/BootVis.asp
Or you can go under your msconfig menu and disable some start up programs to find the culprit, just a hunch though.