1)try to ping and tnsping your remote db to eliminate networking problems. If you get expected responses your network is doing good.
2)try to connect to your remote database using sqlplus.
if it lets you in there are no problems with your tnsnames.ora. That will be another good thing.
If there are problems with two checks above resolve them first. If there are no problems and your db link doesn't work post your error message here and we'll try to help.