Here are some basic troubleshooting steps for Mac and PC:
Visit http://whatismybrowser.com and make sure your browser is updated.
For Safari on the Mac, the cache can be persistent. Try manually deleting the cache files in the hidden folder:
- Develop > Empty Cache, then do steps 2 and 3 below
- Finder > Go (while holding down Option) > Library > Caches. Find the Safari cache file and manually move it to the trash.
- Next, go to Safari > Preferences > Privacy > Details and Remove all Cookies
Let us know if that helps!