For some reason, my samsung monitor started giving me some problems when I use it with my mac pro. It works perfectly on PC, and it used to work perfectly on my mac too, but recently when I connect it to my mac pro, it started showing the screen with wrong resolution when the lid is open, but when I close the lid it gives "not optimum mode" message. I need help.

  • check or replace the cable to/from Mac. – Ruskes May 19 '15 at 6:43
  • It worked, thanks. What is the trick though? How can I possibly know which cable will work? – user2858924 May 20 '15 at 3:39

Normally if you look in the About this Mac, then look how is it identifying the monitor. What does it say about it.

Usually that information will tell you that something is wrong (mostly the cable).

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