Windows cannot start, NTOSKRNL.EXE missing or corrupt

Hi all,
Every time I boot my PC, I always get this error; “Windows could not start because the following file is missing or corrupt:
I tried to fix this problem with an emergency System Repair Disk but all of my attempts failed. I also tried booting while holding F8, and F7 keys but it all failed. The system restored to an earlier point but it could not be accomplished either. I tried to use the recovery console to copy my files across and this was the pop up error message, "access denied".
Thanks!
