Internet connectivity issues

I have been having problems with getting on the internet for months. Have tried many things including buying a new modem, testing with CenturyLink, having my Mac checked out with Apple repair person, all with no better results. Can get on the internet in a flash with my iPad

Welcome to Mac-Forums..

What Mac? What version of OS X? How are you connecting? What happens when you try to connect?

iMac with Yosemite. DSL, Ethernet. The blue line that appears when trying to pull site only comes across about an inch and then locks up.

Did you try going to Networks > Assist Me > Diagnostics ?