Constant spinning wheel of death!

When I start up my iMac, it runs ok for a good 3-4 minutes, then all of a sudden when I try to click somewhere, I get the spinning wheel of death for about 2-3 minutes. Then when I click somewhere else I get another spinning wheel of death for another few minutes. This goes on and on and the computer is basically unusable, unless I want to wait 30 minutes to complete easy tasks that should take 2 minutes.

Any idea what could be causing this problem? I tried resetting the ram by...

Constant spinning wheel of death!