Nonostante avessi sperato per tanti mesi nell'aiuto di qualche volenteroso, la soluzione me la sono dovuta trovare da solo, su alcuni siti stranieri, utilizzando google. Ho fatto quanto consigliato ed ho risolto il mio problema.
Ecco il testo integrale con le istruzioni:
Cause: This error is reported if Disk Manager is detected in the first head (head 0) of the hard disk but is not running.
Solution: If you no longer need to use Disk Manager on your hard drive, you can fix Error 91 by removing the Disk Manager signature from the Master Boot Record (MBR).
If you are not sure whether you still need to use Disk Manager, contact your hard drive manufacturer. They can tell you not only if you still need Disk Manager, but also how to repair it.
If you determine it is all right to erase the Disk Manager signature, perform the following:
1. Create a DOS boot diskette. (You can create a DOS boot diskette by choosing the option to "copy system files" when you format a floppy diskette under Windows 98.)
2. Copy the FDISK utility to the boot diskette.
You can find the FDISK.EXE file in the \Windows\Command directory on any Windows 98 machine.
3. Copy the WRPROG utility to the boot diskette.
Download the WRPROG utility from ftp://ftp.powerquest.com/pub/utilities/
. Once you download the file, unzip it and copy the unzipped file to the boot diskette.
4. With the boot diskette inserted in the floppy drive, boot your computer.
5. Use WRPROG to back up head 0.
IMPORTANT! If the Disk Manager signature is on a drive other than the primary master, you must change the drive's jumpers to make the drive the primary master. This is necessary because WRPROG is only able to back up the first head of the primary master drive.
The correct command line syntax for using WRPROG to back up head 0 is: WRPROG /bak head0.dat
The reason for backing up head 0 is to provide a way to restore its data if you discover later that you still need Disk Manager. The head0.dat file is written by default to the location from which you launched WRPROG (in this case, the boot diskette). You can edit or restore this file later, if necessary. For information on restoring the backup file to head 0, see PowerQuest Solution PR1391.
6. Run FDISK with the "CMBR" switch to clean out the Disk Manager signature from head 0 of the primary master drive.
The correct command line syntax is: FDISK /CMBR 1
NOTE: The number "1" signifies the primary master drive.