Macbook Pro: Yosemite crashing all the time
The first two things I try when running into mysterious OSX problems is "Repair Permissions" and "Repair Disk". After that, reset your SMC and reset your PRAM. Like so...


In OSX, open Disk Utility (⌘ + Space and then type "Disk Utility")
Select your OSX partition on the left, on the right, click "Repair Disk Permissions"
When that is finished, click on "Repair Disk". If that is greyed out, select "Verify Disk" instead.
To reset SMC, shut down your Mac and connect it to power. While it is turned off, on the left side your keyboard press Shift + Control + Option + Power
You might not see anything happen at all. That's normal. 
Next, reset PRAM. Turn on the computer and VERY QUICKLY press and HOLD Command (⌘) + Option + P + R (this takes two hands usually)
Wait until your computer does the restart ding a couple of times, and then release the keys. Let it finish booting.


At this point, any weird issues should be fixed. If you still have problems, you may need to reinstall OSX. If you still have problems after that, you have a hardware issue and need to take the computer to Apple for evaluation and repair.