Wireless connection causing Macbook to freeze

My three-four year old Macbook has just come back from my computer guy for the third time in a month, because of a freezing problem. It crashed before Christmas, and since then it has been completely updated, cleaned, and emptied. Took it back today because it was still freezing once I had opened my internet browser (Chrome) started using my email and then opened a new tab. It seems it works fine for 2 minutes then decides it isn't actually so sure about doing what I want it to.

So I took it back, he joined it to his own broadband, then wireless - everything worked fine. And I mean fine. So I took it home again (narrowly missing throwing it to the curb on my way), started it, and it froze. Computer man mentioned it might have something to do with my wireless connection, so I shut down, and unplugged the modem. Restarted. It all worked a dream. Obviously no connection to the internet, but there was no lag, no freezing, everything opened and quit as it should have.

So I have narrowed down the problem - my Macbook doesn't like my internet connection at home. The problem remains that I have no idea how to fix it.

Can anyone please help me? Any suggestions would be hugely appreciated.

Thank you!!!