Mac display screen works only when external monitor is connected
I have been trying everything over the last 3 weeks trying to fix this computer, and I am now to the last option which is contact you all for an answer.
I have this 2011 Macbook pro 17" on OS X EL captain which gives me a flashing dark Bleu screen on normal mode. the start up is successful, but it just now showing anything on the screen beside flashing every 3 seconds.
1) I connect an external monitor to the DisplayPort the computer On and works just great, with that said, i have both the mac monitor and the external monitor(my TV) work fine. I unplug the external monitor to see if the mac monitor will stay fine NOP it did not. The mac screen went dark bleu and start flashing again.
2) I tried safe mode and the mac monitor works fine with out the external monitor attached to the displayPort.
If i want to use the computer in normal MODE an external monitor as to attached to the displayPort. Even if i turn the external monitor of the computer monitor still work fine, but the moment I unplug the external monitor the dark blue screen comes on, and the computer start to flash and i can't see anything at all.
THANK YOU IN ADVANCE.