\windows\system32\drivers\iastor.sys..... error in vista

Hi,

i have dell inspiron 1520 with vista installed. Some problem happened and now my laptop won't boot.

whenever i try to start the laptop, it get stuck and giving below error:

File: \windows\system32\drivers\iastor.sys

Status: 0xc00000e9

Info: Windows failed to load because a critical system driver is missing, or corrupt.

I don't know why it is coming. I tried everything but this error just don't go. 

I tried starting laptop in safe mode. Its not working. It comes to same page and shows above error.

I tried Vista reinstallation disk to try system repair option but is not booting from DVD also. I check BIOS setup and CD/DVD is first in the boot sequence.

Nothing is working and everytime the same page with above error comes up

Any suggestions how to proceed to get this error removed will be grately appreciated