Very serious issue with connectivity need help

Heya today I find that most apple products cannot connect to the internet at all. Firefox, adium, gmail notifier works, *but Safari, Software updater, iTunes store, etc all tell me I'm not on the internet.*

I've rebooted, etc and nothing seems to work. I ran disk permission fix yesterday and wonder if that did something? Anyone know of a file that handles connections to the programs noted above that may have been corrupted? I have another MacBook which works fine and could likely replace the file on my mac if only I knew which file to do this with.

Ideas are needed ASAP please as most apps I use now won't connect, but again Firefox seems fine.

Note: Software update always suggest to use network diagnostics to fix my issue, but when I tried that the diagnostic said my connection appears to be fine and asks if I really want to run the diagnostic.