i have a imac 21 inch and there's a black spot on top rite on the screen
there is a black spot on top rite of the screen on my imac 21 inch.
iMac, Mac OS X (10.7.4)
You appear to have a faulty LCD screen in your monitor section and would need to take it in to an Apple Store or Authorized Apple Service Center.
Hope this helps 🙂