Help!

I just downloaded and installed avast today on my PC and it has detected my explorer.exe and stopped it from working, now i am stuck and cannot open any files. I try to restart my computer and it just shows nothing except my desktop background.

edit: it also seems that my firefox/chrome/ie are no longer connecting to the internet although i can still use the itunes store :S

Asuming you have Windows XP, boot in safe mode than reboot in normal mode.
Let us know if that solved it.