Every day my computer "freezes" and I get this infernal "not responding"
error.  It wastes an hour or so a day and is quite frustrating.
     I use IE6, Firefox, and Safari, and I have trouble with all of them.
Any ideas on what is wrong?  Thanks.

A) 10 Reasons Why Your Computer Runs Slow - http://www.bestsecuritytips.com/xfsection+article.articleid+43.htm

B) Some classic reasons a computer slows down - http://www.infohq.com/Computer/help/slow-computer.shtml

C) How do you measure the speed of computer processing?

computer processing speed can be measure by Windows itself
through performance feature.....

go to.....

control panel >> Administrative Tools >> Performance......

(My Computer has a score of 3.9).

D) Quite possibly, your internet connection is the bottleneck. 

Thanks artfizz.

artfizz,

My computer is fast most of the time, then it just "locks up" and I get that
annoying error, and often I have to restart the computer.

I am trying that performance test now, but it is not giving me a 3.9 type of score, just a running graph.

Also, what do you mean the internet connection may be the bottleneck, I
have high-speed internet?

"Not responding" means that specific tasks have frozen or are busy.

Have you tried running Task Manager? The Processes tab lets you sort by CPU usage so you see which processes (if any) are hogging the CPU. The Memory column is also interesting. One of your applications may have a memory leak - which would explain why rebooting sorts it out.

The Performance tab will show you graphs which may pinpoint whether CPU or memory is the problem area.

Even though you have broadband, the specific servers you're connected to may be slow to respond, in which case your PC might report the browser was "Not responding".

The first step is to identify which applications are affected.