Changed hard drive. Doesn´t recognize it.

Hi.

I´ve repalced a defect hard drive in a MacBook Pro. But the Mac doesn´t recognize the new one.

I have OSX-install on a USB-drive, and when it boots and I open disk utility, there is no hard drive there. Just the USB-drive.

So I tried to connect the new hard drive to the USB (as an external hard drive), and that works great. I managed to install OSX on it to.

But when i assembly it in the Mac again a folder icon with a question mark appears..

Anyone know what the problem might be?

Also: when I connect the old hard drive back into the Mac, it recognize that one in disk utility...