There will be letters written in small words indicating the location of the switches.
It is a bit different for each motherboard.
Some require the correct polarity, so the negative and positive ends must be attached to the proper terminal.
Be careful, just because the system starts does not mean you have connected the cables properly.
The HDD and Power LED's if they turn on are the indicator of correct polarity.
This should help, ask if you need more help.http://www.youtube.com/watch?v=aE2y30bIejE