Stupid question but do you have a CD in the drive ? If yes, then try to remove it and restart.
Else, you can try to go into the BIOS (press F2 during startup, when the VAIO logo appears on the screen) and check the boot order of the drives. Make sure Hard-Disk is somewhere in the list, ideally at the 2nd place, just after CD. I don't know your model of VAIO, but maybe it has an option to boot from a USB drive. To fix your problem, it is better to put this drive after the hard-disk in the list.
If your VAIO still does not restart properly after that, I am afraid you will have to reinstall Windows with the help of the reinstallation CDs or DVDs.
If your VAIO still does not work after that... probably your HDD or your controller is damaged. I would then advise you to send your VAIO to Sony Support.
Regards,
Thierry
