Replying to Internet Help Needed ASAP!!!

Ok on my laptop a while ago I got a virus. I put my computer on safe mode and ran the Norton Scan and fixed the problem. But after that, neither Google Chrome nor Internet Explorer worked so I stuck with Firefox for a while. Tonight I just downloaded an update for Firefox and now that won't even work. I googled this and it said that the problem might be my firewall settings so I changed those but it made no difference. I am now on my brother's laptop.

Any help is GREATLY appreciated. Thanks!