MS-DOS compatibility mode issues

Updated: 11/13/2018 by Computer Hope

MBR has been modified

Computer master boot record or MBRIf the System Properties window indicates that the Master Boot Record (MBR) has been modified, new software could be the cause of your issue. If you've recently installed an antivirus program, security utility, or drive manager, you may need to uninstall to fix the problem.

If you have not recently installed any of the above programs or utilities, it's a possibility that your computer may have been infected by a virus. Try the below recommended steps.

  1. Boot from a clean write-protected boot diskette.
  2. Once at A:\> type fdisk /mbr and press Enter, this should return you to the A:\> prompt.
  3. Type sys c: and press Enter, once the system has been transferred remove the diskette and reboot the computer.

CD-ROM running in compatibility mode

If the Systems Properties window indicates that the CD-ROM is running in MS-DOS compatibility mode, attempt the below recommended steps.

  1. From Windows click Start, Shutdown, and Restart the computer in MS-DOS mode.
  2. At the DOS prompt type cd\ and press Enter to get to the C:\> prompt.
  3. At C:\> type ren autoexec.bat autoexec.ch and press Enter to rename the autoexec.bat temporarily.
  4. Once this file has been renamed type ren config.sys config.ch and press Enter to rename the config.sys.
  5. Once each of these files have been renamed, reboot the computer to see if the issue has been resolved.

If the issue persists, click Start, Settings, Control Panel, click System, click the Device Manager tab. Click the "+" next to CD-ROM if not already a "-" and highlight the CD-ROM beneath the CD-ROM category. Once highlighted, click Remove, and then restart the computer.

If the issue persists, it's a good possibility that either the CD-ROM drive is bad or Windows is corrupted.

Note: If you want to rename the autoexec and config files back to their original format follow the first paragraph and reverse the file names, as shown below.

ren autoexec.ch autoexec.bat
ren config.ch config.sys

Hard drive running in compatibility mode

If the Systems Properties window indicates that the hard drive is running in MS-DOS compatibility mode, attempt the below recommended steps.

If you are running a DDO (Disk Drive Overlay, a utility that installs and sets up a hard drive using a floppy diskette), contact the hard drive manufacturer for updated drivers.

  1. Boot from a clean write-protected boot diskette.
  2. Once at A:\> type fdisk /mbr and press Enter, this should return you to the A:\> prompt.
  3. Type sys c: and press Enter, once the system has been transferred, remove the diskette and reboot the computer.
  4. Ensure a CD-ROM is installed in the computer, some computers may have a CD-ROM drivers loaded but may not have a CD-ROM installed.
  5. From Windows click Start, Shutdown, and Restart the computer in MS-DOS mode.
  6. At the DOS prompt type cd\ and press Enter to get to the C:\> prompt.
  7. At C:\> type ren autoexec.bat autoexec.ch and press Enter to rename the autoexec.bat temporarily.
  8. Once this file has been renamed type ren config.sys config.ch and press Enter to rename the config.sys.
  9. Once each of these files have been renamed, reboot the computer to see if the issue has been resolved.

Windows 95 users may also be able to edit the NOIDE setting in the Registry to resolve this issue. If you are using Windows 98, see the next section.

  1. Familiarize yourself with the Registry and potential issues with editing the Registry by reading our Registry page.
  2. Edit the computer Registry by running Regedit and open the below path

    HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\VxD\IOS
  3. Locate the NOIDE key, highlight it and delete it by pressing the delete key on the keyboard.

Windows 98 only users

  1. On the Windows 98 CD, open the Tools\mtsutil folder.
  2. In this folder locate the noide.inf file.
  3. Right-click the file and choose install.

If the issue persists, it's a good possibility that either the hard drive is bad/corrupted or Windows is corrupted. We recommend that you first reinstall Windows. If this does not resolve the issue, we recommend that you fdisk, format, and reinstall all the software on your computer.