I have an Early 2011 MBP which has had various issues over the years. About 2 months ago it started crashing more than once a day and occasionally needed to be reloaded from Time Machine backups. Sometimes it is the OS that crashes, sometimes Safari, sometimes Chrome, sometimes Mac Mail...sometimes I don't know... In my ignorance I thought that maybe the hard drive was just old and full of junk; so I bought a new 512gb SSD to replace the original drive and a 500GB hybrid drive to replace the superdrive while I was at it. I changed all the drives and booted from a USB Yosemite startup drive to perform a clean install. There was a few glitches but this ended up working ok. So I know have a clean Yosemite OS and was ready to start over with my new super MBP... However, it seems that was not the problem as immediately everything is misbehaving again and the computer is virtually useless as it keeps restarting every 10mins, crashing programs and generally not working. I have 2.53 GHz intel Core 2 Duo 4GB 1067 MHz DDR3 NVIDIA GeForce 9400M 256MB Any advice much appreciated. Thanks and regards. Matt.