  Though I wasn't looking for a replacement keyboard, if I didn't need one (which is why I asked about a diagnosis), for lack of any other remedy, I bought the Dell Model KP 216 offered on its website. It came with the label on its bottom that said it was a Model KP 216p, different than mine, which had a "t." It worked. While nobody answered the questions about diagnosing the issue, I guess the new working keyboard settles that issue. As to whether the keyboard offered by Dell would work, I guess you could call it the "solution,." That's some handle you got, "Chino de Oro."
My 7 year old Dell XPS 8910 came with a keyboard model number KP216t. Has been working fine for seven years. Recently, keyboard started malfunctioning in a minor way. Hitting "Caps Lock" did not always light up indicator light. Next day, keyboard stopped functioning altogether. Can't even log in. But I was able to log in by pointing the still working mouse to the the "Access" button on the log in page, and selecting the "On Screen Keyboard," by pointing to each letter with the mouse. After log in, computer working fine in all other respects. But I can only limp around using onscreen keyboard. Just can't type using actual keyboard. So computer is largely useless, though apparently working fine, except for keyboard. (From a different computer on same network, I can also access files on the XPS 8910 hardrive). I tried rebooting; didn't work. I tried using keyboard in a different USB port; didn't work. I have no spare working USB keyboard to try substituting--only old style jack plug-ins, which the XPS 8910 can't accomodate, so I can't try testing with a known good keyboard. I also tried running the Keyboard "Troubleshooting" program under Windows Settings, but got no error messages: just an incomprehensible note about "Text"--something or other. Using Onscreen keyboard, I was able to log in and get into Control Panel and Settings. I checked Windows 10 Keyboard Settings, Keyboard Properties. On the Keyboard "Hardware" tab, the box labeled "Devices" had blank spaces under "Name" and "Type". The "Device Properties" had a space for "Mftr" and "Loc" and "Device Status." All three were blank. I checked an older computer with working keyboard for same Keyboard Settings and Keyboard Properties, and found all of the above spaces properly filled in with keyboard data, suggesting my XPS 8910 motherboard is not in touch with my keyboard. I don't know if the keyboard is dead; the USB port is malfunctioning; or there is a motherboard problem. Can anybody diagnose the likely problem from the above information? Also, I noticed that Dell sells a replacement keyboard Model KP 216--same as mine, except without the "t" at the end. Various listings for compatibility state KP 216 is compatible with Dell XPS 8900, but do not list XPS 8910. From this information, can I conclude that the replacement KP 216 will work with my XPS 8910 and I will not need to install any new device drivers? TNX
XPS 8910, keyboard model KP216t apparently dead