Please help me? How do you do a System Restore on Windows vista?

I am so stressed out that my computer will not completly boot up and start windows anymore D: every time i turn it on it stays stuck on a blank black screen with a flashing dash in the top left corner. I dont know what to do or what this means. I dont have any cds either :/ do any of you know how to fix this or do a system restore or recovery wen i first turn on my comp? Ive tried f10 and pressing esc only brings up the boot menu and hasent helped. Pleeasee help im desprate i dont care if everything gets deletes either aslong as windows can run do any o u kno what to do? Thank you!!!! I have a 2006 sony vaio btw