First replace the batteries if it's wireless. If that's not it--Try another keyboard to test.  

@539Sam  A few questions to help with the diagnosis:

1. Are you using a corded, cordless USB or bluetooth keyboard?
2. Is the keyboard / receiver plugged into a USB 2.0 or USB 3.0 port?
3. Is the keyboard / receiver plugged directly into the computer or a hub / extension?

The keyboard is wired.

The keyboard is connected to a USB 3.0 port.

The keyboard is plugged into the computer - no hub or extension.

@539Sam  I'm assuming the keyboard has a USB 2.0 interface.   Have you tried plugging it into a USB 2.0 port?

@539Sam  What do you mean "after restarting XPS 8910"?

Do you mean waking it from sleep/hibernation or clicking Windows Start>Power>Restart?

The PC does have a USB 2.0 port. However, this same keyboard has been plugged in to the same USB 3.0 port for many years, without incident. I'm not confident that will resolve the issue.

Regarding 'after restarting': doesn't matter if waking from sleep/hibernation or recycling the power - same situation: it may work or it may not.

It is possible that something is failing within the keyboard/cable.  Have you another keyboard that you can try with the computer?

@539Sam  If trying a different keyboard doesn't help:

• When was last time you replaced the motherboard battery? CR2032 3-volt coin cell battery, ~$2.
• Open BIOS setup and make sure USB wake support is Enabled. Don't change anything else, but save the change, if any, before exiting setup
• Back at the desktop, open Device Manage
  1. Expand list under USB in Device Manager
  2. Double-click each USB entry and look for a Power Management tab
  3. Uncheck the box" "Allow PC to turn off..."
  4. Repeat for all USB entries with that tab
  5. Do the same for all Human Interface Devices with a Power Management tab in Device Manager
  6. Reboot

Does that help?

The battery has never been replaced. I'll tray that along with other settings.

Thanks for suggestion. Thought SupportAssist would have detected that.