MBP 2010 external monitor not waking Up until recently my MacBook Pro 2010 worked fine with an external samsung monitor, using a mini display to HDMI cable. At the time I was running Mountain Lion. Then a few months ago, still running mountain lion, the monitor started not waking up with the mac. The only solution now is to unplug the monitor and plug it back in. I have to do this 2 or 3 times now before it will work. Also, now it no longer works in target display mode: if i close the lid of the mac with an external keyboard and mouse, everything sleeps. Then when I open the lid, the monitor doesnt wake up. 

Unplugging and plugging in the cable cannot be doing it or the socket many favours. Also I am ending up leaving my mac on all the time so I dont have to go through this routine (set to never sleep). 

I dont see why, running the same OS, why this would just start happening. Perhaps Apple updated something that caused this problem?

Does any one have any ideas? this is highly annoying. I was thinking maybe a Mavericks upgrade might fix this issue, but then it might cause others. Ideally I don't want to do that. I have tried resetting the SMC and the NVRAM.
Based on your reply, first to check is the cable or connector.
Software does not randomly connect or disconnect and because you say it works after you plug-in and un-plug the cable a few times it works... the cable might be broken.

If you have a replacement, try it - else you could buy one (and return if it does not solve the problem). Based on your reply with VGA it works fine, I would definately buy a new cable/connector.