iMac extremely slow

[ferrarofilms]

Trying to do a 30 sec video with FCPX and the Imac is running desperately slow. First I thought it was FCPX, deleted Preferences with pref manager but no better. Then I realised it is the Imac, cleaned everything, Ram 10gb free out of the 16, processors(Quad 3.40)over 80 iddle, 700gb out of 1TB free on system disk, 2Gb Graphics, op temp 65 celsius CPU. Recently upgraded to last 10.8.3 OS. Restarted, same problem. This is a late 2012 Imac.
Any hint?
Thanks

 

[KevinGrabher]

Is it slow in any application?
Is it slow only with graphicly intense tasks?
It it slow when working with big files?

 

[fastlanephil]

Disconnect from the internet to make sure you're not being slaved.

Try resetting the PRAM and the SMC.

Repair permissions in Apple's Disk Utility.