Try a different DNS server.
Open System Preferences > Network > Advanced > DNS
Click + and type in this address:
Click + again and type in this address:
Quit and relaunch Safari and try those sites. I can access them both on Safari.
If that didn't help, try here > Safari 6 (OS X Mountain Lion): If Safari can’t open a website
Hi! I have the same problem. Macbook Pro 13inch (2012 model), just upgraded to OS X (10.8.4) and have Safari 6.0.5 installed, but Safari is not loading any webpages as they should appear, ie. the webpages loaded are all in html format, no logos or pictures, just text on the page. Any ideas on how I can fix this? Am new to OS X and upgrading on my Macbook.