......
AHEM.
Anyway, I'm guessing you can access all other internet stuff OK since you haven't said anything. Therefore it must be something wrong with steam. There's a file somewhere, and if you delete it, it checks your steam directory for any 'broken' files or something, and re-downloads them if need be (i think).
If I find the files, I'll tell you

.
EDIT - file is: C:\Program Files\Steam\ClientRegistry.blob
1. Close steam
2. Delete file
3. Open steam, and file should re-download.
Maybe make a copy of the file somewhere else before trying this though, just incase
