Q: Connection failed-----assistance please

I'm having a problem with my connection to the Internet. I'm running a home wired LAN consisting of a Macbook 7.1 running Lion, a Macbook 2.1 running Ubuntu 11.10 and a Dell running XP. The router is Cisco Linksys. What initially happened is there was a service problem in the area. So the next morning I got up and all the lights were go on the modem yet I was unable to connect to either the mail server or the Internet. I called the ISP and we tried cycling and connecting directly to the modem but couldn't get it to work. A call was made to Cisco and I was referred back to the ISP. The only other thing I can figure is something weird happened when I uninstalled and reinstalled Avast AV for Mac last night. Is there a way I can check if Avast is preventing me from accessing the Internet by blocking some port or something. I had a similar issue in the past where I had installed Avast but still had some pieces of AVG installed. Once I removed those I was able to access the Internet. Maybe something similar has occurred. I'd like to eliminate that as a possibility before the cable technician shows up tomorrow morning. It could be the modem; tht has happened before but I'm not sure. At the moment, I'm connected on my Ubuntu machine using a public WiFi. Interestingly enough, when I tried to access the Internet through WiFi using my newer Macbook, I was unable to. I essentially experienced the same issues I had on my home LAN. Any ideas?