I'm at work now, so I can't get to the ebay site to check cable. Don't know what version of windows you have, but you'll have to go to:
system ;
hardware ;
device manager ;
and under "ports-com-lpt" you should see your cable listed as com 1 or some other number. Main point here you need to check to see if your computer recognizes your cable and assigns it a com port number. Then in your radio software you must assign it the same com port number.If you plug it in to a different USB port the next time you use it, it'll change the com port number.
Edit: what I left out is your cable should have come with some driver software, which is usually specific to different windows types (95-98-me 2000-xp-etc..) another thing is some software isn't compatible with 64 bit computers.. Try the above and let us know what happened.