Keyboard and mouse not recognized after boot-up!

Ed, in reply to your points:

1. I am *not* able to get to the BIOS config screen, because my keyboard is not being recognized. Is there any way to get around this?

2. I cannot use Remote Access either, because I've disabled it on my PC, for security reasons. In my 25 years of working with my own PC, I've never allowed anyone, including a tech from Microsoft or Dell, to remote access my PCs. Paranoia? Perhaps, but it's never been a problem, until perhaps now. (I'm running Win 10 Pro, and my wife's PC is running Win 8.1 Pro, btw.)

Thank you for any help---much appreciated!

Thank you, Ed! I'll call Dell, but any further assistance from you or your buddy would be most appreciated!

Thank you for all your extra effort on my behalf, Ed! And thank you, AndreTen, too! I'll try these things and post back. (I'm on hold with Dell now, btw.)

OK, so here's where I am now:

• After spending an hour-and-a-half with a Dell "Premium Support" tech, mostly trying things and variations on things that I'd already tried, the main problem has *not* been resolved.
• However, after about an hour with no progress, on the advice of the Dell tech, I powered down the PC and held the power button down for 60 seconds and, a few minutes later, also moved my monitor's HDMI plug from the "discrete" port to the PC's "integrated" (motherboard) port, and as a result I *can* now get into the BIOS (via the F2 button) and the boot menu screen (via the F12 button). The Dell tech said that he thought that either holding down the power button or moving the HDMI plug (which seemed an odd step to me) did whatever it was that allowed the PC to access the BIOS setup and boot menu.
• After an hour-and-a-half, the Dell tech basically gave up and---after mentioning that his research (Google?) had found that some other users had experienced this same issue after a recent Windows 10 update---suggested that I call Microsoft.
• When I went into the BIOS setup utility, the boot order options that I found there were:
  
  • Windows Boot Manager
  • Onboard NIC (IPV4)
  • Onboard NIC (IPV6)

There was no reference in the BIOS boot order setting to either a USB drive or the DVD drive with the Active@ Boot Disk DVD. However, when I used F12 to access the boot menu, the Active@ Boot Disk ("CD ROM") drive was shown in the list, along with the other three options shown above. That is of some interest, as I'm thinking that perhaps I could use some Windows recovery tools on a disc to access System Restore, but I soon realized that Active@ Boot Disk was of no use for this particular problem, because it doesn't give me access to System Restore.

Now that I can access the BIOS, am I correct in thinking that there's *no* need to remove the motherboard (CMOS) battery, or to move the jumper plug back and forth?

So, should I now follow AndreTen's instructions and disconnect the internal drives, so only the USB will remain? But what about the fact that the boot menu (F12) did *not* show the USB drive with my Windows installation files? Would AndreTen's method still work somehow?

And am I correct in thinking that the Windows install files that I put on the thumb drive at the end of the Windows Store download process have recovery tools of some sort there? I can't remember whether they do or not. If they don't, how might I get the needed repair tools to put on a thumb drive? And will I be able to access the thumb drive given that the boot menu (F12) screen did not show the drive when I had it plugged in? Does the boot menu perhaps show a thumb drive *only* when it has the correct, bootable files on it, or should the thumb drive show up there regardless of what's on the thumb drive? Should I be focusing on a recovery disc, instead of the thumb drive? If so, what source(s) would I use for that?

Sorry for all of the questions here! And thanks for any continuing assistance!

George