...My Computer Is not more Booting...

Dear Friends,
I will need your help and suggestions again.
I After intallation of Windows Xp,the light went off.
After that anytime i boot the PC,it is showing me this message:

FILE IS MISSING OR CORRUPT:
\Windows\system32\config\system
start windows setup using setup CDrom.
Selct"r" at the first Screen to start repair.

On repairlevel it is ask me which wondows to i want to run or load?
and it shows (this)\>

How can i correct the file missing to make my PC working again without reload the OS?

Thank you for your advise,
johnii