Follow these steps to troubleshoot the error messages Operating system not found or missing operating system.
IMPORTANT: If model-specific information is required to complete any of the steps in this solution, refer to the operating instructions supplied with the product.
- Because each of these steps represents a possible solution to this issue, check the computer status after completing each step.
- If this issue occurs on a notebook computer, ensure the appropriate AC Adapter is being used by comparing the model number on the AC Adapter brick to the AC Adapter listed in the computer Marketing Specifications under supplied accessories.
- Disconnect all external devices connected to the computer.
- Remove all optical drive media (CD/DVD/BD) and USB Flash media from the computer.
- Remove any additional hardware that was installed in the computer.
- Reset the computer BIOS to the default values .
- After resetting the BIOS, ensure the Hard Disk Drive (HDD) is detected in the BIOS.
IMPORTANT: If the HDD is not detected in the BIOS then a hardware failure has occurred and the HDD may need to be replaced.  Go to Parts and Accessories.
- If the HDD is detected in the BIOS but the operating system still will not load, perform a System Recovery .
- If the issue is still unresolved even after a System Recovery, service may be required. Go to Product Repair.