Intriguing! Usually you know when somethings using it!
I don't know if there is anyway of detecting what app may be using it.
Is the laptop running NT4?
I know there was some cases with certain older Dell Laptops getting
funny with comm ports. I remember we had one that would could
only be setup either for NT4, or for DOS but not both, through
some strange settings in the BIOS.
Hyperterminal would indicate your running 2k/xp?
All I can suggest is check that the Comm port is shown OK under
Device Manager, see if there are any IRQ Conflicts if you can.
I've just done a few searches and apparently some PCMCIA devices
do want to share IRQ's and cause problems..
I presume you've tried a restart to kill anything that may have been
running?
Failing all of that...
Have you got a floppy drive and an old dos boot disk lieing around?
If your confident you could boot your laptop into pure dos from the
floppy.
I've found some free software here:-
http://www.taltech.com/freesoftware/fs_sw.htm
called ComShow which by the look of it will do the same thing as
HyperTerminal which runs in DOS.
With Dos there's no worrying about drivers for serial comms, and it's
doubtful
that anything will conflict with them by default.
If on the other hand you've never touched DOS in your life that might
be a bit over the top,
in which case we'll try something else =)