HP 550 w/ (best recollection) approx 2G prcssr & 4M RAM. 32-bit Vista Home Basic SP1 (can't GET to Vista display to see if updated). It's had McAfee or Symantec anti-virus loaded for college usage. CompUSA purchase-July '09. LCD screen replaced @ HP-summer 2010. This laptop played fine for 1 yr w/ daughter at college. Came back from HP after screen change & daughter advised it stopped working within a mo. After replacing blown ext pwr supply/charger to get pwr, I consistently get Vista not loading with: "Win failed to load because critical sys driver missing or corrupted: File:\ $WINDOWS.~BT\Windows\system32\drivers\iastor.sys"

Have 3 original DVDs: OS DVD, App & Driver Recovery DVD, & Supplemental SW (trial Office '07). There is an "iastor.sys" file on the 'Supplemental' DVD.

From reading online/your FORUM, it appears possible/probable virus possibility? I should copy the Supplemental iastor.sys file & attempt to replace/install on the laptop? If so, how to load /replace the missing/corrupt original file?

Thanks for your forum. iastor.sys is your hard drive controller driver.

Copy iastor.sys file from supplemental DVD to USB drive.
Plug the USB stick to bad computer.
Boot from your Vista DVD, access command prompt and copy the file from USB stick to Windows\system32\drivers folder