Server Application Not Available

I'm getting Server Application Not Available Error when I try and run any of my web applications. Can anybody tell me why I might be getting this error.

One other thing does anyboyd know what font is used for the <code> tag is visual studio help i have a currupted font and i can't read the code on one of the fonts.
-JoeWere you ever able to run aspx pages before? If not then try running "aspnet_regiis /i" from the framework install directory. If yes then please look up thefollowing post.

Hope that helps
Kashif