Printer trouble-shooter all tried out... Help!

I've tried everything in the printer trouble-shooter, with
no luck. It's definitely the computer - I've tried two
different printers and checked that they work with another
computer. I've swapped the cables, so they are also
working.

I've uninstalled the LPT1 port and the printers and re-
installed (several times...) but still no luck. This also
confirms that the printer is communicating with the
computer, as both printers tried are recognised by the
computer when plugged in again.

The computer prints to a network printer okay.

The only other clue is that, after producing the 'print
failed' message, the printer subsequently throws one page
with a single hieroglyph in the corner when the (both do
the same) - seems to be when the printer is disconnected
from the computer.

I've run out of ideas - can anyone help?!