Sounds like you're covering ground similar to that I traversed a while back...with nary a clue as to what was happening or, when it was over, had happened.
There are many things you can try, and I'm certain that others will kick in with ideas, but having "been there," the best suggestion I can make is that you try changing your AirPort Radio Mode in AirPort Utility > Wireless.
Towards that end, can you tell us both which band you're running in now and which bands your router supports, i.e. 802.11n (which can run in either the 2.4 or 5GHz band) or 802.11b/g compatible (which is limited to the 2.4GHz band)? (The info can be found at the above-captioned location on your MacBook.)
The new Great Equalizer is the SEND button.
In Memory Of Harv: Those who can make you believe absurdities can make you commit atrocities. ~Voltaire