Which version of LW are you using? If you're using LW 4, see below.
Go into your account, open LW & go tools > options > advanced > firewall. Make a note of LW's listening port. Close LW.
The listening ports on your account & your Dad's account need to be different.
Go into your Dad's account, open LW & go tools > options > advanced > firewall. Change your Dad's listening port to 65000 (as long as the listening port on your account wasn't 65000) > apply > ok.
Restart your computer. Now see whether things are any better
If you're using LW 5 then please let us know, because the options are different in the new version.