If you have a copy of your hard drive on an external drive that's bootable, I'd suggest booting from that drive (plug it into the USB port and hold alt/option at startup to select that drive), and seeing if your internal HDD shows up as a 2nd mounted hard drive.
Assuming you have an external enclosure, you also might want to try ripping the internal HDD with the files you need out of your MacBook Pro, putting it in the enclosure, and mounting it as an external drive on another Mac. If you do that, you should be able to see your documents and a few other things, at least.
One logic board failure is pure chance. Two sounds like maybe there is something wrong here. Are you plugging in directly to the outlet in the wall without a surge protector? Older homes this can be a no-no. Unreliable power can kill a machine. The other thing, that commonly happens is people don't understand how fragile their cables are. See my FAQ*:
If you feel you have damaged your cord, or your port, and have another logic board replaced, keep that in mind for the future. Do not under power your notebook. MacBook Pros require a full 85W.