When I go on the internet with Microsoft internet Explorer viset a few sights, and then go back to the desk top and click on start to do something else I notice the button is highlighted but nothing happens.  If I wait for as much as 60 sec. it will come back.  If I tray to use the control alt. del it says that it is internet explorer not responding.  If I keep trying to get it to stop I will see the dos prompt and the only way I can get it back is to reboot the computer.  Most of the time I have learned to leave it along and it has always come back.  Why is it doing this?

   Internet Explorer 7 has some memory problems but you should not see them after only visiting a few sites.
   What you describe sounds like memory problems.  It sounds like something is using most of the memory, which leaves little memory to accomplish everything else.  This slows everything down drastically.  That is why it takes so long for the Start menu to come up.  That may also be why you are having the not responding problem with Internet Explorer.
   What happens when you go to Windows' Task Manager is that it sends out a message to each of the programs that are running and waits for them to respond back.  If the program is not working it will not respond back.  But there is also the possibility that the program is working but is too busy to respond back.  If the program has been slowed down 100 or 1000 times slower because there is not enough memory to run it, it will take a long time before the program gets to its process which sends an answers back to the Task Manager.
   The question then is what is taking up all of the memory.  The answer can be a lack of memory on the computer, other programs running, a virus, or any number of other things.