buying a switch or hub is one solution, but it won't necicarily 'fix the problem'. You will still need to configure the media players to correctly connect.

Has this exact config ever worked in the past? Or have you reciently re-arranged? Is yours or your Dads comp new? Reload OS or media players?

{Internet}---[cablemodem]----[Dads PC]---[your pc]
Is this correct?

If the picture is correct, & all questions answer (Y-N-N-N) to the above, is your Dad running NAT software?

I'm thinking he "may have" blocked your media ports. Now... do not get mad... it's only a thought. It may not be happening.

keep us posted.