hdd listed bios wont boot

[gyula.kocsis.1982]

My father in law has 2 HDDs in his machine and it has been working properly since 2015. As of yesterday, the machine will boot only for one HDD, which has win8 on it ( the other has win 10 on it). The BIOS sees both the HDDs but regardless the boot order it will only boot from one. When using the win 8 all the files are accessible and can be edited on the other HDD. Ran chkdsk and no problems were detected with the HDD. What shall I do to make my HDD bootable?

Thanks you.

 

[R_1]

will not boot. as in flashing cursor in the top corner of screen, skips the drive and boots to the other, says missing or invalid boot loader?

http://www.thewindowsclub.com/repair-master-boot-record-mbr-windows
a walkthrough on how to repair/replace the master boot record on windows 10. if the files on the drive are accessible maybe the boot record is damaged.

 

[gyula.kocsis.1982]

Nothing flashes no messages just boots the WIN8 immediately regardless the given order.

Will check that link later thank you!

 

[R_1]

Nothing flashes no messages just boots the WIN8 immediately regardless the given order.

Will check that link later thank you!

what happens when the only drive connected is the windows 10 drive.
shut down the computer
remove the side panel
touch unpainted screw to ground yourself.
find the power cable to the windows 8 hard drive and unplug it. wide black plug with red, yellow and black wires
boot the system
the system can now only boot to the 10 drive
are you getting a message now?