If your logic board is bad and you have to replace it, then it is probably more cost effective to go buy a refurbished MacBook instead of shelling out $500 or so to get a replacement logic board.
However, it may be worth a shot to open up your laptop again to make sure everything is plugged in correctly. It would be a shame to throw a laptop away because of a simple loose connection. You can also try [http://support.apple.com/kb/HT1431|resetting the PMU]. It may not fix the problem, but it is worth a shot and it is free!