Suddenly my two hard drive configuration does not work

hi
I am not sure my title is clear so let me explain. I have set up two internal hard drive months ago. I have a 250gb ssd and the original 750 gb HDd. They worked fine for months
Yesterday out of the blue while I was transferring data from the ssd (mother drive) to the HDd to improve performance the computer relaunch and suddenly did not see the ssd...
I opened everything and unplugged the second drive and restarted
Then after a rather long time for a ssd the computer started normally. Everything works apparently. So I turned off my computer and restarted after replugging the second internal drive and now again the ssd does not show up. I have nothing
It does not show up in disk utilities...
Any suggestion ???

My mac is from late 2012
I have the latest update of os since I did it yesterday (July 19th 2015)

 

Ok
I waited for thirty minutes and it restarted "normally"
I still think it is acting weird and slow. I will finish the update then do a trouble shooting with the commands esc+command+option to clean the scm

 

I try to reset the PRAM... That was a bad idea
I am back to the installation of the HDd like it does not see my ssd anymore...
That does confirm that something is odd. How on earth this can make a ssd disappear?
Any idea? I am going to wait a bit and restart to see...