virtual down key stuck

I have an IMAC-intel with a wired keyboard. The down arrow is stuck *virtually*. In various orders, I:

Discovered the "stuck" key (the down arrow) with the keyboard logger

Changed back to the original factory options in the keyboard

Rebooted too many times to count.

Unplugged the wired keyboard and plugged it back in. Didn't work

Tried the PRAM reset thing - I think it's an urban legend - no beep, no effect.

Pried off the key, cleaned it, but that didn't work.

And this - ha ha - UNPLUGGED THE KEYBOARD, but *that* didn't work. The "key" was still stuck, according to the keyboard logger!!

Another person on the web has expereicnced this problem for *years*. I've only had it for a few days.

It was suggested to another poor soul that they shoud re-install their OS.

Any help would be very much appreciated.