My macbook will not connect to the internet!!!

So I just recieved a used macbook from ebay today. I was so excited because everything was working perfectly - internet and all!! Then, after about 20 mins of being on the internet, the connection was lost. Now everytime I try to connect it says "Connection Timeout". All other devices still work perfectly on the same wifi. I have researched this all day and tried everything.. Nothing works. Someone please HELP!!!!!!