It could be a problem with the (internal) hard disk. Run the Dell diagnostics, and even if they say it's OK, try another disk.
About three weeks back, I have upgraded from Windows7, 64 bit on DELL Inspiron One, to Windows 10. Just before the upgrade, one day while taking back up on external HD, it could not be ejected easily. I shut down the computer and then removed the HD. Thereafter, frequently I have been getting following error message: "Reboot and select proper boot device, or insert boot media in selected boot device and press a key.". Since DELL also did not provide support service for this problem, I upgraded to Windows 10 with the hope that I could start with clean slate, as if the OS were loaded afresh. There is no other issue with Windows 10. But, I continue to get same error message now and then. I have to do some circus or reboot repeatedly before the computer starts correctly. I shall be grateful if the members out there can throw light on this problem, and how to overcome it.

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