[H] No keyboard in DOS Full Screen on WINXP SP3

[nobozoz]

I have some WIN2k SP4 and WINXP SP2 systems where my DOS program works 
perfectly fine after it opens in Full Screen, but in WINXP SP3, the 
program displays fine, but ordinary (single alphanumeric) keyboard entry 
is unresponsive.

WINDOWS' CTRL+KEY and ALT+KEY combinations DO work, however.
I'm baffled. Any suggestions?

Thanx,

Jim