Cannot access some web-sites... help.

I have a MacBook Pro running OS 10.6.

There were websites I used to visit without any problems (like www.livestrong.com and gigapedia.com). Then one day (nothing changed hardware or software-wise), I could no longer access these sites from my computer.

My friend came over - with his PC - and was able to access it from my network. I was also able to access the sites from my wife's iMac G5 and iPod Touch (same network), but I still cannot access them on my computer using ANY browser (Safari and Firefox). I cannot access the site from anyone's network either --- making me think my MBP is doing something weird with the Network Settings.

I keep getting:
"The server denies connections. The server might be too busy or might be disabled. Try again a bit later."

I have installed Glimmerblocker on Safari and AdBlocker on Firefox, but turning these off does NOT change my results.

What do I need to reset or what did I do to cause this? How do I fix this?

 

Thank you! This works!

Sorry about the overly-creative title, but I had posted this twice previously (using proper titles) with 0 replies and figured to try with something else.