I cant access the internet

At first FF would give the error cant find server. I have internet connection but wont let me on line. Explorer also wont let me on line says this page cant be displayed. I tried restoring computer back before this started and it would work for a little while then start again. I tried diagnosing and it said nortons wasnt installed properly but I cant fix that without the internet. Now when I click on firefox it gives the error couldt load XPCOM. I tried saving firefox to a flash drive from another compter to load on this one but it gives the error Network error (-2146697211) encountered, install aborted. I have tried to fix it for two days and I feel I am out of options. Please any help is greatly appreciated Thank you