Please hold down the option key as you click the wifi button on the top right corner as seen [http://grab.by/57xj|here], as rab has said, your laptop is not wireless N compatible, but the intermittent signal is another problem. The fact that you were running on the wifi for a short period of time means that it is most likely broadcasting B and G. Sorry but I won't give you the steps to access the router as you do not own it, and b/g is enabled by default so unless the owner turned it off, it should still work.