XP Pro firewall seems to have dissapeared!

ok, within the past month my desktop has been doing some odd things like not allowing full connectivity to the internet or within my home network. It has also had issues running certain programs (like installation software or some programs just simply crashing every time I try to run them). The strangest thing is that Windows Firewall appears to have been removed from my computer. When I go to my control panel and internet connections, I am used to seeing the little brick wall icon for the Windows firewall...but there is nothing but a blank space where it used to be. When I move my mouse over the space it changes appearance like there is still something there but nothing happens when I click on it. When I right click it gives me the option to make a desktop shortcut so I tried that and the shortcut went to nothing.

I tried going to my add/remove programs but can no longer go into that either. I click on it and get that loud error sound windows give you and nothing pops up. When I right click on one of my LAN connections to try and go to the internet security settings, the right click menu pops up for like one-tenth of a second then goes away.

I'm afraid some vicious virus has come on my desktop, but I cannot install anything it seems that would defeat it. Any ideas?????