Windows 10 will not boot, cannot access anything as monitor keeps going into sleep mode

I am trying to use a Windows 10 PC which was working fine but has not been used for a while, probably a year or more. When I first turned it on I managed to get into the BIOS, reset the time and check hard disks and boot priority. I then rebooted but received error message "Reboot and select proper boot device. Insert boot media in selected boot device and press a key" I realized I might have set the wrong hard disk for my boot drive and tried getting back to the BIOS. I now cannot do anything as monitor keeps saying entering Sleep Mode and shutting down completely. Can anyone advise how I might be able to get out of this vicious circle?
Many thanks
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Tyler BrooksNetwork and Security ConsultantCommented:
I would start by removing it from power completely, unplug it and hit the power button a few times. If that doesn't work then I'd suggest clearing the CMOS and/or pulling the CMOS battery.

What video interface are you using? I recently came across a model that I was only able to get video out of the onboard VGA port until resetting the BIOS to defaults (it's also had an onboard DVI which didn't work until after the reset).

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Scott CSenior EngineerCommented:
Try swapping or adding in a video card.  

It's possible the boot drive is bad.  Sometimes if a spindle drive sits for a long time the arm can freeze up.
Hello ThereSystem AdministratorCommented:
Check if your HDD is properly plugged into MB. Use another power connector.
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RaminTechnical AdvisorCommented:
I would Replace CMOS Battery with a new one first,   because you mentioned you needed to re-set the time on that PC,  so the Battery is dead and cannot keep (save) data related to Boot Sequence or other BIOS necessary settings.

As the next step you can detach RAM module(s), remove the dust and attach again.  if there are more than one Module then try them one by one and retest.
i agree with ramin
the battery is in most cases a CR2032 model, and should read 3V min; cost = +/- 1 $
medcomputersAuthor Commented:
I would like to award equal points to each of the 5 contributors to my question but am not sure how to do it. I think I will strip this computers down and start again as I can now see several possible problems. I would like to close this question down now as I have more important problems on my main PC and would like to open a new question regarding this issue,
just pick one first as best solution, then award the others
medcomputersAuthor Commented:
Thanks for all your suggestions. I am going to rebuild computer with a new motherboard.
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