Applications freeze until window is moved

I've been having an ongoing problem with my system. Safari, as well as other applications keep freezing, and the only way to unfreeze them is to grab the open application window at the top of the screen and move the window. Though it happens with other apps, Safari is what I use most, and it happens every 10 seconds to 1 minute. As an example, I can type a web address or search term in the address bar and hit enter, and nothing will happen until I move the window and then it will load. Or scrolling will stop working on a page until I move the window, or I can click a link, but it won't launch until I move the window.

I run multiple accounts on the mac, and each has the same issues. I've repaired permissions, have installed Saphos and run virus searches (nothing found), have removed Safari extensions, have unplugged peripherals, have viewed activity monitor seeing nothing of significance, and have reindexed Spotlight. This has been done to most of the individual accounts as well. Running Safari on the guest account works fine.

Another non-Safari example is changing user accounts. After selecting an account to login to it often freezes before I can enter my password and I get a beach ball that doesn't spin. I have to press the power button for a second to force it to sleep, and then wake it up to try to enter a password in time.

Any suggestions are appreciated.