MacBook Pro boots after stop sign appears?

Hi there,

Here's the rundown: I have a mid-2012 13" unibody macbook pro. A couple of months ago I changed the original drive for a Crucial SSD, successfully, although I had to update the SSD firmware to fix lagging/freezing issues ; then a month ago, I updated to OSX Yosemite, with TRIM enabled, also successfully. About 2 weeks ago I upgraded the RAM from the original 4G (2X2G) to 8G (2x4G), again, successfully. Today I got a Patec HDD caddy in the mail, as I had planned to replace the optical drive with the original macbook pro hard drive. I followed a tutorial I found here, on this website and upon completion, when I tried to reboot, I was greeted by a grey stop sign on a gray screen, with an occasional flash of the macintosh apple... after about a minute and a half or two minutes, the login screen appeared and everything worked fine. I then shutdown the computer and rebooted once more, to see if there were any changes and the same thing happened.

Second to last thing I need to say is that I forgot to disable TRIM before messing with the hardware and it was advised to do so.

Finally let me apologize for any weirdness in syntaxe or wording ; english is not my first language.

THANK YOU IN ADVANCE!