I have an early 2009 24 iMac and a late 2009 27 iMac. The 27 has that common problem of the monitor going black. And staying black. Computer runs fine, but screen goes black.
The monitor of the 27 goes black. Has been black for months. So I use an external LG monitor.
Yesterday, I hooked the 27 up as an external monitor to the 24. IT WORKS FINE. So.
So. The brains of the 27 will show visual to FROM another computer. And TO another computer. But it will now show visuals on itself.
What can that be?
iMac (27-inch Late 2009), OS X Mavericks (10.9)