A1242 Wired Keyboard stops entering characters, Reboot fixes (for a while)

I can't find any threads discussing this issue. (I do give up easily)

This problem started last week after two years with this keyboard/iMac pairing and working fine.

After a period of inactivity (over night) the wired USB apple keyboard (A-1242) stops entering keyboard characters.

The trackball works normally.

Swapping USB ports doesn't fix the issue.

Restarting is the only thing that fixes fixes the problem, tenporarily.

Resetting the PRAM hasn't fixed the problem, it still looses keyboard inputs after a long rest. (Cursor continues to move and cursor commands work fine.

A different Apple usb (older) keyboard works fine when the A1242 has temporarily died.

Something dies between the A1242 and the iMac and requires rebooting to fix.

Any help or ideas would be dearly appreciated.

Thanx

GG