I have a 2009 MBP (7,1) which I recently upgraded the hard drive to a Crucial BX100SD.
The hard drive was configured via. a USB to SATA cable on my desktop machine. I used a Flash install of Yosemite to get the OX onto the new hard drive.
After completion, I was able to successfully boot to that hard drive on my desktop via the USB to SATA cable.
I went ahead and then swapped the drives in the laptop and booted it up. At about 30% the start up hangs on the grey screen with the apple logo. I tried booting into recovery, and it hangs at about 20%, never successfully loading the recovery.
So far I've reset the PRAM, and tried booting directly into recovery via. Command+R and also using the option key to select the recovery directly. I've also tried to boot directly from the flash drive OSX install, but it doesn't seem to work on the machine. However, I can successfully boot the flash drive on two different desktop machines.
Starting to run out of ideas on how to make this work, I'm extremely perplexed as to why the SSD and Flash Drive boots just fine on my desktop, but not in the Laptop.
Edit: My assumption is that there's some sort of incompatibility with the hardware and OSX 10.10.1, I'm going to try a boot of Mavericks from a flash drive I'm creating now and see where that gets us.
Second Edit: Apparently RAM I installed months ago didn't want to play nice with the new SDD. Switching back to the old ram got the computer to boot no problem. (Weird, because I previously had no issues with the RAM before upgrading the SDD)