I don't understand the 2 letters puzzle..
All I can see is "BJAD", I have no idea what to do.
The chart on the second letter tries to tell you that A = 0, B = 1 and c = 2. If you continue this pattern and with the entire alphabet, you'll have a number for BJAD which is 1903. Type that into the cellar keypad.
Eventually, I'll implement a puzzle answer hint thing. Or a walkthrough.
Sorry if you were having trouble