Not physically, but digitally.

So i turn on my PC, it's a new build. It takes ages to start up, much longer than normal. Then when i log on i find out it's as if my second HDD isn't there. It's where all my documents are, just not my OS.

It's not in BIOS, disk management, my computer. tried another cable and SATA port, no luck. What on earth can i do?! I need that stuff!