Did you check the bios to see if the port is enabled?
My Dell XPS8700 desktop doesn't recognize my Sandisk Ultra II 480G SSD.  I am running Win 8.1.  File Explorer can't find the SSD and neither can the Control Panel "find devices". The Sandisk SSD Dashboard can't find the SSD either.  It is connected to the SATA port 2 and I have checked the power and SATA connectors.  Any ideas?
XPS8700 doesn't recognize ULTRA II 480G