After using my computer for a while, I find that I can speed up the computer by turning it off for at least one minute, then turning it back on.

I am guessing that something accumulates in the RAM and slows the processes down.

By turning it off and then back on, it "dumps" or gets rid on what is slowing down.

I have tried various memory managers at no avail.

Can someone explain why this happens and maybe suggest some utility that will to the same thing?

This has happened to ALL computers I have ever had, so it is not unique to my present computer.

   If you are not shutting it down for days at a time, that is normal.  My guesses as to what can cause that are:

• Memory used by an application is not properly freed up when the application closes.  RAM cleaners do not work in freeing up these because they cannot distinguish between the inactive unfreed memory and active memory used by running applications.  One way around this is to avoid using an application that seems to not clean up memory after itself.
  
• Windows drivers are being improperly used by applications and so mess up and then do not perform properly for subsequent applications using them.
  
• Background processes are running and accumulating.
  
• Problems with virtual memory.
  
• Windows processes running in the background that do not run until the computer has been on for a while.
  

   I recommend that you do a Shut Down at least once a week (daily is best).