SSD Dropping out

Hey guys, I have a sandisk extreme SSD (240GB) and for some reason whenever I try to use it it drops out and doesn’t come back. Can anybody help me with this? Because I am limited to using a WD Caviar blue 1TB and I would much rather be using the SSD.

Whoops… I meant WD Caviar green

I have bought another SSD now so all is fine.