MacBook Pro (2011) 13" keeps crashing with Yosemite 10.10.2

My MacBook Pro8,1 (early 2011) "Core i7" 13" started crashing after I upgraded and installed the free Yosemite 10.10.2 from Apple. Has anyone else with a similar model MacBook Pro laptop experienced this problem in general? Problems with Yosemite started soon after the upgrade install... the startup would get to full boot up after several restarts then crash after a time. At first I thought it was a conflict with other applications. Then after days of trouble shooting and even changing to a new Samsung EVO 250 SSD the problem still recurred repeatedly. I have re-installed the original install CD numerous times checking disk utility, partitions, etc. and got Snow Leopard 10.6.6 installed OK. Then I would update all that I could clicking updates on the Apple menu icon up till OS 10.6.8 and some other applications. Up till that things seemed to be OK. As soon as I downloaded Yosemite OS 10.10.2 and installed it...then all the crashing problems began. I could get into safe install every now again then restart only to get in a startup crash loop. I've repeatedly check my new SSD with disk utility and volumes are OK. I've run virus checks with no infection. I've run a hardware test (provided on one of the original CDs) with only good result. So I'm really baffled when my understanding is MacBook Pro of my vintage can accept OS 10.10.x as it doesn't appear to be OK on my laptop. Perhaps it clashes with my virus checker (MacKeeper) or some other application. Can anyone shed light on this problem or have a similar problem?