Macbook Pro crashes instead of sleeping

My Macbook Pro 13" Late-2011 model with 2.4GHz is having a problem. This problem has occurred a few months earlier and it happened again. When I try to put my mac to sleep, or if it puts itself to sleep, instead of the sleep light fading in and out and the mac waking up when I open it, the computer continues to make noise wit the sleep light on for 10-15 seconds, then the sleep light fades out completely. When I open my computer again, nothing happens. After I press the power button, the comuter loads up as if it had died. When the final bar in the loading process is half white, but not completely loaded, my mac repeatedly makes three beeps in coordination with three flashes of the sleep light. I then have to turn off my computer and turn it back on for it to open up. I cannot remember the circumstances of the first occurance, but it went away eventually. Now it is back. It first reoccurred when I used the Deep Sleep widget to put my computer into deep sleep, then brought it up to Idylwild at about 5000' elevation and with a lowest temperature of 28 degrees. I brought it up placed next to me in a strong Thule case, and it did not suffer from physical damage. When I tried to wake it up from Deep Sleep, the problem occured and has continued to happen every time it goes to sleep in Idyllwild and since I returned to my near-sea level house.

Any idea what it is or how I can fix it?

Much Appreciated