NETWORK/INTERNET FAIL lol

Hey there, I am currently having problems with my network/internet.
-comcast cable modem
-linksys router

I dont know if i set the network up wrong but i followed everything in the installation process. My network is fine for LAN and connects to the internet but will disconnect 20 - 30 mins of using it getting dectect computer settings. The Comcast technician said for me to hook it up directly and if it does the same thing that it's the modems fault. I just recently returned one of their modems for a new one and the problem still occurs. When connecting directly to my computer I am unable to connect to the internet i.e. (limited connection or no connection) but if i directly connect to my ps3 it works but only for about 10 - 15mins then reciever network error ect. Thank you for your time