My iMac 27 inch late 2013 wakes from sleep mode with black screen.

[jimmyusmc]

My iMac 27 inch late 2013 wakes from sleep with black screen. The only thing that works is the arrow cursor and the black screen only last about 10-15 seconds and then it goes back to normal. Any idea how to fix this? I have a base model running maverick Apple techs over the phone told me to reset and then want me to restore back to factory settings. Thanks in advance for you input and help. -Jimmy

 

[nambuccaheadsau]

Have you ever increased the memory in your iMac?