Monitor not responding to mac mini. PLEASE HELP! :(

Hello,

I have a mac mini, 2011. For some reason, the VGA monitor connected through a mini display port adapter is not working. The only thing I know of the monitor is that it is a Princeton. The monitor worked perfectly for about 10 months now, but for some reason whenever the mac falls asleep the monitor will not boot up. It flashes on and off, saying no signal, going to sleep. Then it goes to sleep, turns on again, and does the same thing. I tried rebooting the mac, it shows the gray screen with an apple logo and a loading pinwheel, then the screen turns blue, and goes off. I've even tried booting it while holding command, option, R, P as suggested by an apple support employee. It worked the first time, but them the problem happened again. I have tried another monitor, a samsung SyncMaster 2233, and it did the same thing. This is really annoying, I need a permanent solution for this problem. I cannot mess with my mac turning it off and on constantly trying to make the screen work.