its good thing it startup in safe boot though
so startup your computer in safe mode
then from Start>Control panel> Automatic upate> and turn it off then reboot and see if it startup in normal mode
also you may do system restore
Start > All programs > Accessories > System tools> System restore >
and pick eariler date when your computer was working fine and after rebooting it should work fine
of both not work for you.. so tell what happens when you startup in normal mode?
try and feedback