After replacing the power supply in a desktop PC, a technician powers the system on. POST completes, but a black screen displays the message "Operating system not found," and the boot process halts. Which of the following is the MOST likely cause of this symptom?
The SATA or NVMe drive that holds Windows is not detected because the data cable is loose or the drive has failed.
The user's Windows profile is corrupted.
The print spooler service is disabled.
A recently installed video driver is incompatible with the GPU.
The error appears before Windows starts, so the system has not yet loaded user profiles, drivers, or services. It usually means the BIOS/UEFI cannot locate a bootable operating-system partition. A loose or failed hard drive (or SSD) prevents the firmware from detecting the system drive, triggering the message. Corrupt user profiles, disabled services, or incompatible video drivers occur only after Windows loads and therefore would not generate this pre-boot error.
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