So you had what is called a "dual boot" configuration set up and working before the change. Usually that means that Win 7 was on your machine first, and later you installed Win 10 and told it to create the ability to choose which version to boot. VERY often when that is done you actually have two boot devices (two HDD's, for example), each with one Windows version on it as a bootable Partition. So, is that what you have - two drives with different Windows versions on each?
If yes, then what I suspect has happened is that the BIOS Reset process set the normal boot drive to be the one that happens to have Win 7 on it. I suspect further that the OTHER boot drive (that has Win 10) also has the files needed to accomplish the Dual Boot system and offer you the choice. But the reset BIOS is not trying to boot from that drive.
So, try this. Go into BIOS Setup. Check what drives you have. Now look at where you specify the Boot Priority Sequence, and write down which is the first boot device, and the second one, etc. If I'm right, the first thing it tries to boot from is the older drive with Win 7 on it. Change that to the drive that has Win 10 on it, and MAYBE set the Win 7 drive as the SECOND boot choice. Remember to SAVE and EXIT. The machine will save this new setting and boot as directed. I hope it will now offer you the choice of which system to boot into.
If that does NOT work, go back into BIOS Setup and re-arrange your Boot Priority Sequence to be as it was before this new change, then SAVE and EXIT. Then at least your machine will continue to work as it has recently, even if you can't boot into Win 10.
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