MacBookPro crashed with pixel disturbed screen and 3beeps I have 
MacBook Pro

15-inch, Early 2011 

Processor  2 GHz Intel Core i7

Memory  8 GB 1333 MHz DDR3

Once a week it crashed with beep sound ( 3 times ) beep - beep - beep

Then pixel in the display ever time it crashes is as shown in screenshot
The only way to turn off the the laptop is by pressing power button for 8sec.
There is most probably a problem with your RAM.
You can run a full test on the RAM with something like Memtest booted off a CD. See here for Mac instructions.

You may find just one RAM module is corrupt and you just need to replace or remove it. It might also be that the RAM has become unseated, try taking it out and putting it back in again to see if that is the case.