The 320 (and 312) don’t have hard drive or power LEDs that connect to the board so you don’t have to worry about that. IIRC, there are two USB cables (4 pins) and the power (two pins) cables that need to be connected.
The USB (one is for the IR/VFD the other is for the SD card slot) just plug onto internal USB headers; the power can go either way and if the USB devices don’t show up or the PC won’t boot just flip it around (connect them one at a time). It’s not going to do any permanent harm to put them on wrong.
