MBP will not connect to external monitor

I am using 13" late 2011 MacBook Pro. I used to be able to connect it to an external monitor, but recently, I have not been able to.
When I plug it into the monitor, the screen on the MBP will flicker blue and freeze, but the computer never detects the monitor.
I have tested the HDMI cable, and that is not the problem. Any ideas what could be causing the problem?

Morning aeck692,
Thanks for using Apple Support Communities.
For troubleshooting on this, take a look at this article:
Apple computers: Troubleshooting issues with video on internal or external displays
http://support.apple.com/kb/HT1573
It may not hurt to reset the Mac's parameter RAM.
Resetting NVRAM / PRAM
Shut down your Mac.
Locate the following keys on the keyboard: Command (⌘), Option, P, and R. You will need to hold these keys down simultaneously in step 4.
Turn on the computer.
Press and hold the Command-Option-P-R keys before the gray screen appears.
Hold the keys down until the computer restarts and you hear the startup sound for the second time.
Release the keys.
If the display does not come up, was previously set to an unsupported resolution, and still results in no video:
Start up in Safe Mode.
Hope this helps,
Mario

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MBP will not connect to external monitor

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