I have been running Ubuntu 18.04 without problem for several months on a Lenovo T540p. This morning I tried to log in and had some trouble - the computer kept rejecting my password. Eventually I turned on my on screen keyboard (through the universal access menu at top) and was able to put in my password that way. It turned out that the shift keys on my keyboard no longer work.
This link Shift keys not working properly suggests that i try re-configuring my keyboard keymap. It took me a while to try this, since my shift key wasn't working, but with an exteral keyboard, I worked through the first two steps. Then I saw the comment that this caused another user's 18.04 to stop booting. Suffice it to say, I am nervous about working all the way through these.
Edits in response to a comment by @Terrance:
I can use the shift key if I plug in an external keyboard. If I boot from a live CD or into recovery mode, or into an earlier installation the shift key on the laptop's keyboard doesn't work, but the external one does.
This seems like a hardware problem. In that case though, it seems strange to me that both shift keys would have failed at exactly the same time. Is it time to retire my computer (or always use an external keyboard) or is there anything else I can try? Thanks.