Most likely the SATA ports are turned off in CMOS/BIOS.
you need to shut the computer completely down and enter setup.
Depending on the make and/or model of the computer this is usually hitting a single key usually escape
or one of the function keys and going through the setup menues to turn the SATA ports on.
This chance to hit that key usually appears on the "Logo page".
That being said IF you turn them on then the computer will probably expect to see something connected to them
HOW the computer reacts to this again varies on specific make or model.
I know on most Dells i'll tell you during startup that "drive x not detected" and willl USUALLY continue booting
On others it'll trigger another chance to enter setup.
On most HPs and Compaq computers it'll cause a hard stop and REQUIRE you to either enter
setup or accept the new configuiration by hitting the F1 key.
Again this varies model to model.