9-pin D Connector

I have a Sharp ZQ-520 organiser, the contents of which I wish to backup to my PC, which is undertaken via a lead to the 9-pin D connector on the PC, and software supplied by Sharp with the organiser. The PC runs on Windows 98SE and has a Pentium III processor. For some reason, PC and organiser do not wish to communicate with each other.

How do I narrow down the fault to :-
1. Problem with the D connector on the PC
2. Software issue (although the PC appears to be trying to communicate with the organiser once the ?synchronisation? process is started).
3. Problem with the connecting lead.
4. Problem with the organiser.