Can’t browse the internet

I have a system running on windows 7. I connected a USB modem provided by my GSM provider and browsed successfully the first time but suddenly i can’t browse anymore. I tried every possible thing suggested by many fora but to no avail including uninstalling norton, disabling firewall, winsock fix, ip config……….. I even installed an antispyware but i can’t still browse. I tried pinging google,com and it replied. I don’t know what else to do.