When Scandisk won't run properly or doesn't detect problems that you know exist on a hard drive, the operating system is often to blame because it can interfere with Scandisk’s ability to detect problems. Although you can get around this problem by running Scandisk in DOS mode, there’s a better solution: Remove the hard disk from the PC and install it as a slave drive in another PC.
By doing so, you’ll have full access to the drive from Windows, without Windows getting in the way of your ability to scan and recover files. When the drive is installed as a slave device, all of the system files on that drive are seen as data, and there’s no danger of these files being opened or closed while you’re trying to scan and fix the hard disk.
A few issues to consider
Before you implement this technique though, there are a few things that you need to consider. First, the operating system makes a big difference. The operating system on the machine being used to make the repair must be able to read the partitions on the malfunctioning hard drive. For example, a machine that’s running Windows NT 4.0 can't read a disk that’s formatted using FAT32. Likewise, you wouldn’t be able to fix a NTFS partition from Windows Me (without third party tools).
Also, you must remember that in a situation like this, antivirus software can be a double-edged sword. It's absolutely critical that you scan the malfunctioning hard disk for viruses. In fact, a virus can actually cause a hard disk to appear to malfunction. At the same time, though, antivirus software can seriously interfere with your efforts to scan and repair the hard disk.
For that reason, after you’ve transplanted the malfunctioning hard disk into another machine, I recommend running a full virus scan on that machine. Scan all drives and all partitions, even if you’re sure the machine is virus free. Once you’ve completed the scan, disable your antivirus software until you scan and repair the transplanted drive.
When Scandisk just isn't enough
Of course, there’s a chance that even on a different PC, Scandisk may simply be inadequate for detecting and fixing the hard drive. If this happens, I recommend buying a third-party disk utility, such as Norton Utilities, Winternals Disk Commander, or Acronis Recovery Expert. If one of these products isn’t in the budget, there are free alternatives. You can find several good data recovery utilities at Bootdisk.com.