Error Message "Invalid System Disk" After Setup Reboots

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• Microsoft Windows 95
• Microsoft Windows 98

SYMPTOMS

During the first reboot in Windows 95 Setup, you may receive the following error message:

   Invalid system disk
   Replace the disk, and then press any key

CAUSE

This error message may be caused by one of the following situations:

• The system is infected with a boot-sector virus. This error is known to be caused by the AntiCMOS.A virus.
• The system is running virus-protection software.
• The system is using hard disk management software (such as Disk Manager, EZ-Drive, or DrivePro) for hard disk geometry translation. These tools provide support for hard disks with more than 1024 cylinders.
• Setup was unable to copy the system files to the hard drive.

RESOLUTION

Use one of the following methods to correct the problem.

Systems Infected with a Virus

Use an anti-virus program to detect and remove the virus, and then reinstall Windows 95. Boot-sector viruses infect computer systems by copying code either to the boot sector on a floppy disk or the partition table on a hard disk. During startup, the virus is loaded into memory. Once in memory, the virus infects any non-infected disks accessed by the system.

Systems Running Virus-Protection Software

Boot the system using the startup disk created during Windows 95 Setup. Use the SYS command from the startup disk to restore the system files to the hard disk.

Some computers use built-in anti-virus software that must be disabled in the computer's CMOS settings. For information about changing CMOS settings, consult the computer's documentation or manufacturer.

Systems Using Disk Management Software

Windows 95 may not in some cases detect disk management software and may overwrite the master boot record (MBR) information. Refer to the documentation for the disk management software you are using for information about restoring the MBR.

Also, check the Setuplog.txt file for the following statement:

   FSLog: BIOS Heads=:64:, BootPart Heads=:64:

Reinstall the Windows 95 System Files

CAUTION: If you are using Disk Manager or any other disk drive overlay program on a hard disk, make sure that the overlay driver is loaded before you use the SYS command on that hard disk. If the overlay driver is not loaded and you use the SYS command on the hard disk, the drive may not be recognized as being partitioned by the disk drive overlay program and you could experience a data loss or inability to boot from the drive.

1. Boot the system using the Windows 95 Emergency Boot Disk.

2. At the MS-DOS command prompt, type the following lines:

         c:
         cd\windows\command
         attrib c:\msdos.sys -s -h -r
         copy c:\msdos.sys c:\msdos.xxx
         a:
         sys c:
         attrib c:\msdos.sys -s -h -r
         del c:\msdos.sys
         copy c:\msdos.xxx c:\msdos.sys
         attrib c:\msdos.sys +s +h +r
   

3. Remove the disk and reboot the computer.

   ARTICLE-ID: Q129260
   TITLE     : Windows 95 Setup: Description and Troubleshooting Steps

MORE INFORMATION

The third-party products discussed in this article are manufactured by vendors independent of Microsoft; we make no warranty, implied or otherwise, regarding these products' performance or reliability.

REFERENCES

For more information about boot-sector viruses, please see the following article in the Microsoft Knowledge Base:

   ARTICLE-ID: Q82923
   TITLE     : Methods to Detect a Boot-Sector Virus