Help, don't know what to do, in panic!!!

Someone, please help me!! Somehow my laptop downloaded a virus, i'm not sure what kind of virus but seems to be winning. My internet is so jacked up that i can't get on it, i'm using my mom's laptop right now. it's running pathetically slow, WAY slower than normal, and i can't back up files when i attach my external drive. To top things off, when i click my START menu button, it only gives me the option to click on the internet or to shut down or activate my most recent programs. Everything else is just gone! My All Programs button, my Control Panel, my Run..., my My Computer button, all of it...Need help badly:cry. In the corner next to my time it says VIRUS ALERT, this System Alert bubble keeps popping up out from my taskbar, keeps having this pop up window telling me to download some crap, and keeps trying to access the internet, but it can't b/c it's running so slow. Sorry if this problem has been posted before, couldn't find another post that had the same problem with both the START menu and internet.