I had a pre-built PC I got from best buy, i'm trying to install the motherboard into a new HTPC case. I've looked on the internet for a manual but no luck. Its an Acer AM1100-1302B
Also there are no words printed on the motherboard either indicating which is what... I took a picture you can see here. They are color coded so I hope that helps, but the colors on the board do not match the colors of the wires.
Use the reset and hardrive led leads next to each other, and the power switch and power led's side by side on the inside row of pins. It won't hurt to test them out as long as you are using the correct group of pins. They are all low voltage. When you have it right, all the case lights will work, and you should be able to power down any time without the system freezing up.
The last poster has it right. The power switch lead is the on/off. If your case power led has 3 pins with the middle wire missing, you can make it a 2 pin lead by forcing the wire back out using a small paper clip, then carefully snapping it back in the center.