OK, how about trial and error? Don't worry as you can't hurt anything until the board powers up and even then it is difficult.
First locate the power-on pins. Starting on the end opposite the missing pin, short pairs of pins until it powers up - use the power switch connector and put it on pairs of pins on the sides - lets number them even on one side and odd on the other - the header should at least have a mark denoting the pin 1 end - could be a white arrow pointing to pin one or a white line on or under the pin 1 end of the header
_ 2___8______18
_ |_|_|_|_|_|_|_|_|
_ |_|_|_|_|_|_|_x_| In this diagram, usually 1-3 or 2-4 will be power-on and the other will
_ 1___7______17
be reset.
try pins 1 and 3 first, then try 2 and 4 do not try cross-row options as the connections are almost always in the same row. As soon as you find the power up pins, go into the BIOS setup and set it to boot first from floppy or bootable CD (whichever you have handy). Put your bootable disk in and boot up from it so you can test the other pins. Generally, the reset button will be on the opposite row from the power pins. Try that first - locate the power LED prior to trying more pairs to locate the reset as that is the only one that should have power on it with a permanent ground pin two pins away (if you have a meter, it would make that easy - Sears has a nice kit on sale for $12. this wek - don't forget to buy the needed battery (usually 9V)). if no meter, just try each triplicate of pins with the power LED, first in one polarity - then the other. Usually that will be the pins on both sides of where the pin is missing. Usually the HDD LED will be on the other side on the end - will be hard to locate until you are doing something that accesses the HDD a lot - but you can put that off until then as it isn't that important. Generally the speaker positive side is always on (either 5 or 3.3V) and the beeps are controlled thru switching the speaker's ground pin on and off. So locate the pin with power on it and you're done. You get the gist. If you're lucky, somone may happen along who actually owns the board. But if not - you now have a Plan B...
.bh.
FYI - Chaintech has been out of the mobo business for some time. .bh.