Windows 7: corrupt volsnap.sys file preventing bootup

Hi,

Tried to reboot my laptop this morning and it went into startup repair. The diagnostic messages in the log said that both the acpi.sys and volsnap.sys system drivers were corrupted.

I brought up a command window under Recovery options and it placed me in the x:\windows\system32 folder. I wasn't sure why the drive was x: and when I tried changing it to c: it let me do it but when I tried dir to list its contents it said it was System Reserved and it looked empty. I figured that x: was actually the os drive and for some reason had been mapped to x: within the recovery tools.



Anyway, cd'ed into the x:\windows\system32\drivers directory and replaced the acpi.sys and volsnap.sys files with good one's from a USB memory stick (gotten from my desktop PC) , but upon another attempt at rebooting the laptop it failed for the same reason and after inspecting the dates on the acpi.sys and volspan.sys files I could see they had been replaced with the older currupted versions again.

How can I replace these files so they are accepted by the system and not replaced with the corrupted ones?

TIA,
Nick