My system looses OS, I need to recover it, what can I do?

i dont understand:

if you lose the "System32" ore something i mean Blue Screen and cant acces?

if the answer is Yes: Easy, get Ubuntu 12.x put on a USB drive, then do all the work without format you only need "Try on Windows" when you can get on that, you can search all your documents and then you are ready to format

and if you mean try to repair Windows?

use the Windows CD, DVD to do that, enter first to the boot menu and start with the CD or DVD then Use the option "Repair Windows" and sometimes it works

Greatings from Guatemala!