PC and Monitor (PLS READ FULL DESC) (Shirley B90)

Happy New Year folks,
I have a Compaq PC and ACER monitor. I got the PC through this website a couple of months back. I built it up by adding a 500 GB SATA hard disk drive and 4GB DDR3 RAM. It was working when I installed W10 Pro but the PC was quite slow so I tried installing a lighter version of W10 instead.
I get this message 'No boot disk detected or the disk has failed'. I don't think it is hard disk failure as it was working fine when I tried it on my other PC but you can get a HDD for around £3 from Computer Exchange (CEX).
Includes the following:
Compaq PC tower that has 500GB SATA HDD, 4GB DDR3 RAM, AMD E1 Processor - comes with power cable
ACER Monitor - has some dead pixels around the edges which is only noticeable when the screen is black - comes with power and VGA cables

Collect from Shirley. Preference given to those who an collect asap.

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