It sounds like it's looking for a network boot instead of the hard drive. Check the boot sequence in the BIOS. How do you know when a politician is lying? His mouth is moving.
If this system was working previously then there are a few possibilities. If the bios settings were not altered then the hard drive is not being detected. This can be because of drive failure, Cable (Power or data) faulty or dislodged, or motherboard fault. Goin' Fishin' (Some day)
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