need help tethering works on laptop but not desktop

ok so heres the scoop i have a 1gb plan and some tethering code attached to my account and im somehow able to tether on my laptop (which is using desktop manager 6) but want to tether on my desktop (which is using desktop manager 5.0.1)/

For some reason it isnt working. tried rogers tech support online and by phone throughout this whole thing (over an hour) and they said something about the ports should be com5 and com6 (which is on my laptop) but on my desktop its com3 and com4. they wiped my phone thinking it was that, uninstalled then reinstalled desktop manager, restarted my computer and did numerous battery pulls but no dice. any ideas on what the problem could be?