Mac air... internet Slows down after a while please help

[jfanzen]

Hey everyone I have a mac air... I found out a lot of people were using my internet at my apartments... so i went to http://192.68.1.1 and turned it to wpa personal so no one else uses my internet. Everything was fine then after like 5 minutes of using my internet i click on something and it just loads and loads and tells me to check internet connection or firefox cant find website... blah blah blah... My brother who has a mac pro has not problems.. its only my computer.... The internet is connected... also... the 192.68 address... will not go through... also.. when i turn it of and on the internet is fine... but after 5 minutes the same thing happens... can someone help me out... also.. lets not forget im not very good with computers... so talk to me like im 5 thanks.. guys