Connect Mac to an external display My system is OS X Yosemite. When I connect MBP to a monitor, the monitor shows no signal error and the MacBook screen also becomes black. Disconnecting will not make the MacBook screen normal again. I have to force it to shut down and restart. 
I also don't have the "detect display" option in system preference -> display. Does anyone have the same problem?

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MacBook Pro 13-inch, Mid 2012. Processor: 2.5 GHz Intel Core i5. Memory 4GB 1600 MHz DDR3. Graphics Intel HD Graphics 4000 1024 MB. The cable is VGA-mini displayport (not Apple brand, but worked fine with projectors before). The monitor is AOC E2752VH (model #: 270LM00004)
Those specifications and those of the cable and monitor indicate that it should work.

You could try resetting the SMC on that Mac by shutting down the Mac holding down the Shift+Control+Option keys and the Power button at the same time. Wait 15 sec and then turn it back on.

Failing that you could start in Safe Mode by holding the shift key while booting (booting will take a lot longer) and try plugging in the monitor then.

Failing those I would try another adapter, preferably one with an all digital signal path like a Mini Displayport to HDMI or DVI-D