12.4 Windows 9x Troubleshooting Problems
12.4.2 Error codes and startup messages
Error codes that are generated at system startup usually indicate hardware problems, configuration problems, or boot up problems that are associated with the operating system. Any errors that occur with these problems will result in a startup failure. These problems must be fixed in order for the system to start properly. If one of these errors appears, use the emergency boot disk to boot the system and begin the troubleshooting process.

"No operating system found"
If the "no operating system found" error message appears during startup, the most likely culprits are either a failed hard drive or a damaged or corrupted master boot record (MBR). This error message might also appear if the command interpreter (COMMAND.COM) file is missing. To troubleshoot the problem, first check to make sure that the hard drive is properly installed and that all the cables are properly connected. If the problem persists, start from a boot disk containing FDISK.EXE, then use the
fdisk /mbr command to fix the master boot record on the hard drive. At this point, it may be necessary to run diagnostics on the hard drive to determine if a hard drive failure has occurred.

Note: The error message displayed will depend upon the BIOS and the specific version that is on the machine.

"Windows Protection Error"
This error can occur when a computer loads or unloads a virtual device driver (.VxD). In many cases, the .VxD that did not load or unload is mentioned in the error message. In other cases, it may be impossible to determine which .VxD caused the behavior. Windows Protection error messages can occur under several conditions:

  • A real-mode driver and a protected-mode driver are in conflict.
  • The registry is damaged. 
  • The WIN.COM file or the COMMAND.COM file is infected with a virus, or is somehow damaged.
  • A protected-mode driver is loaded from the SYSTEM.INI file and the driver is already initialized.
  • There is a physical input/output (I/O) address conflict or a Random Access Memory (RAM) address conflict.
  • There are incorrect Complementary Metal Oxide Semiconductor (CMOS) settings for a built-in peripheral device (such as cache settings, CPU timing, hard disks, and so on).
  • The Plug and Play feature of the computer Basic Input/Output System (BIOS) is not working correctly.
  • The computer contains a malfunctioning cache or malfunctioning memory.
  • The computer motherboard is not working properly.

"Illegal Operation"
This error message means that the program in question is having a problem. The "illegal operation" designation covers a wide range of errors. It may take some time, patience, and troubleshooting to pinpoint the cause. The most common causes of an illegal operation include problems between that program and a software driver in the operating system, or memory-management problems between the program and an open program in the background. Problems and conflicts with different Dynamic-Link Library (.DLL) files, which are added to the system when software programs are installed, can also cause illegal operation errors. Hardware conflicts, defective RAM chips, and program bugs can also cause the error. To pinpoint the cause, ask some questions. Has this program always worked but is now crashing unexpectedly? Has anything, like new hardware devices or software, been added lately? Tracing the advent of the problem to a specific event may help to narrow down the list of likely suspects. The "Illegal Operation" error can be generated due to an incompatibility of a printer driver as well, even if this error is not generated when printing.

"A device referenced in SYSTEM.INI, WIN.INI, or Registry is not found"
The WIN.INI file contains parameters that can be altered to change the Windows environment and software settings to the user's preferences. The WIN.INI file is a software initialization file for Windows. It contains information about some Windows defaults, the placement of windows, color settings for the screen, available ports, printers, fonts, and software applications. The SYSTEM.INI file contains hardware setting information for the drivers that Windows uses for configuration. When the "A device referenced in SYSTEM.INI, WIN.INI, or Registry is not found" error message displays, it usually means that these files contain an entry that is no longer installed in the system. To fix this error, open the files and edit them to remove the lines that are referencing the hardware or software.