Computer files can get damaged in several different ways: by a power interruption, by virus or badly written software, by bad RAM or by physical damage to the hard disk.
Symptoms:
The laptop starts as usual but when Windows starts to load it goes to black screen with either “UNMOUNTABLE_BOOT_VOLUME”, “hal.dll is missing or corrupted” or “windows\system32\config\system” (or similar) is missing or corrupted. These error messages indicate a corrupted filesystem or a failing hard disk, about 40 / 60 chance.
Troubleshooting:
The easiest way to diagnose and possibly fix corrupted filesystem is to start the computer from a bootable CD, then scan the hard disk for errors. If the scan completes successfully, the registry can be restored by hand and the computer can be scanned for viruses.
The best way to do that is first to make an UBCD4WIN CD on another computer and start your PC from it. To make the UBCD4WIN you will need a working computer with high-speed Internet and CD burner, and a standard Windows XP SP2 installation disk, “Home” or “Pro”. It is possible to use XP installation disk without a service pack or with SP1, but it will have to be slipstreamed to SP2 before building UBCD4WIN (see http://www.ubcd4win.com/ for details). This is by far the best bootable CD for Windows users, as it will let you use your computer as usual. It comes with hundreds of free programs and utilities that can help you fix almost all software problems.
After starting your computer from UBCD4WIN, go to “Start” button -> Command Prompt and type chkdsk /r /f c: (in the black window that opens). This is the native Windows command for scanning and fixing your “C” drive. Depending on the size of your “C” drive and the number of files you have, this may take from about 30 min. to over 2 hours and if there are errors on the HD – even longer.
If chkdsk shows a lot of errors, especially in “Step 1″ or “Step 2″, you will have to replace the hard disk. You still should let chkdsk finish fixing the disk, so you are able to eventually copy your files to the new disk later on.
If the hard disk is very damaged, chkdsk either won’t start scanning at all or won’t be able to finish scanning it. It will get stuck and stop working. In this case the chances of you being able to copy your files to the new HD are slim. If your files are very valuable, you may consider sending the HD to a data recovery service, however the prices for that start at about $500.
If chkdsk was able to finish scanning the HD showing many errors, shut down the computer, replace the hard disk (if it’s easy to do so) and reinstall/restore Windows, or send the computer for service if it’s still under warranty. Then mount the old HD in an external USB box and try to copy your files. If you have chosen “Make my account private” when you were choosing your password, you won’t be able to open the old “My Documents” folder. Here are some instructions on how to fix that.
If chkdsk finished without any errors, or just 2-3 errors, you can assume that the hard disk is working properly. The file corruption may have been caused by freezing, restarting by itself, improper shutdown of the computer (pulling the cord), viruses or sometimes by bad RAM. If you suspect that there may be any viruses on your computer, use one or two of the antivirus programs that come with UBDC4WIN. To do that you will need Internet connection.
If the error message that prevented the computer from starting was “UNMOUNTABLE_BOOT_VOLUME” or “hal.dll is missing or corrupted”, you can try restarting the computer as normal (not from the CD). If it still doesn’t start (both in normal and safe mode) you will have to reinstall/restore Windows, but first backup your files.
If the error message that prevented the computer from starting was “windows\system32\config\system (or similar) is missing or corrupted”, now you should restore the registry files by hand. To do that (still from UBDC4WIN) navigate to “C: -> Windows -> System32 -> config” and rename software to software.1 and system to system.1. Open another window and navigate to “C: -> System Volume Information -> _restore{any-numbers-and letters}”. There you will see a few folders named “PR” + some number. Sort them by date (right-click on empty space and choose “Arrange Icons By -> Modified”) and open one that’s about a week old. Inside you will see one folder and many files. Open the folder.
Now copy the files named _REGISTRY_MACHINE_SYSTEM and _REGISTRY_MACHINE_SOFTWARE to the other open folder (windows\system32\config). Then rename them to only SYSTEM and SOFTWARE (no extensions).
Restart.
* The Windows System Restore is useful in only two occasions: the one described above and if a driver or Windows update doesn’t install properly and the computer wouldn’t start in normal mode but still starts in safe mode.
