Missing Operating System After Setup Restarts Your Computer

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Article ID: 134708 - View products that this article applies to.
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When you are installing Windows 95, you may receive one of the following error messages the first time Setup restarts your computer:
- Missing Operating System
- Invalid System Disk
When you receive one of these error messages, the computer no longer boots from the hard disk.


There is an incorrect value in the Partition Boot Record (PBR) on the hard disk. Any computer with a mis-match in the number of read/write heads reported by the Partition Boot Record and the system BIOS will likely have this problem.

If there is a mismatch in the reported number of read/write heads, the C:\Setuplog.txt file contains unequal numbers on the following line:
FSLog: BIOS Heads=:64:, BootPart Heads=:64:


To correct this problem, follow these steps:
  1. Restart your computer using the Emergency Startup Disk.
  2. Use the SYS command to transfer system files to the hard disk. For example, if the Emergency Startup Disk is in drive A, type sys c:.
  3. Remove the Emergency Startup Disk from the floppy disk drive and then restart your computer. Setup should continue.
If you do not have an Emergency Startup Disk and cannot obtain one, start your computer using a Startup disk from your previous operating system (such as MS-DOS). Use the SYS command to transfer the system files to the hard disk, restart the computer, and then run Windows 95 Setup again.


This issue is known to occur on Leading Edge Fortiva 5000 computers. The PBR on Leading Edge Fortiva 5000 computers returns a hexadecimal value of 40 heads. The actual value is 20.

For additional information about the "Invalid system disk" error message, see the following article in the Microsoft Knowledge Base:

Error Message "Invalid System Disk" After Setup Reboots


Article ID: 134708 - Last Review: November 15, 2006 - Revision: 1.1
  • Microsoft Windows 95
kbenv kberrmsg kbhardware KB134708
Retired KB Content Disclaimer
This article was written about products for which Microsoft no longer offers support. Therefore, this article is offered "as is" and will no longer be updated.

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