When I switch the pc on, my monitor goes off and on several times with a loud click. Any suggestions how to fix that?

I think this could be a problem with the monitor's electronics.  I had a problem similar to what you are describing with a new monitor that I bought last year (2005).  The tech at the manufacturer's help desk said the monitor was defective and needed factory repair.  I was able to return it (because it was so new).  

Good luck