Problem typing "t"

I cannot type "t" when entering text of any kind. I THINK that I caused the problem after I was finding my way around the "shortcuts" in edit\preferences, and I have a memory that it involved defining something that involved "t" - sorry, but I cannot remember exactly what I did.
Here's what happens:
if I type "t", nothing happens. The next letter keystroke I hit does nothing, but a following letter appears immediately after, So, if I type :
b it shows as "b"
"bt" it shows as "b"
"btd" it shows as "b"
"btdd" it shows as "bd".

The same thing happens when I hit the "t" key in capslock
Hitting "t" key in caps lock - nothing happens
Hitting any key next, nothing happens.
Any subsequent key then works OK.
ie TDD shows as TD.

The only way I can get "T" is
The only way I can type "t" is to caps lock, and , then hit capslock again to get back to lower case to continue.

I tried resetting shortcuts to default, but no good.
I also had a good look in the shortcut tab in preferences, but there is no shortcut "t" there.
As it involves text, I don't see that uploading a file would help, but let me know if this information is not enough.
Thank you, Rod