Safari :: Can't Click On New Web Pages

Often when I click on a weblink, Safari tries to load the new page, but nothing. The web address shows up in the bar at the top, but no response. It happens often. But, even when I'm having trouble, navigating around in some closed community like Facebook works fine, so it's not an internet connection problem. (I thought it was a connection problem at first--poor wiring?--but since I can move around in Facebook, I'm dismissing that.)  Also, it happens both when the computers are connected through the routers or directly via Ethernet to the AT&T U Verse modem.  

This started when we switched from Comcast cable to AT&T, but there have been numerous Safari updates since then. I don't really think it is a Safari problem. The only PC on the home network doesn't show this problem (but it is an older, slow PC); both Macs on the network exhibit the problem. Happens whether we use the ethernet network or go wireless (non-Apple routers).  

Info:
iMac