All we know is that you have a keypad that doesn't work. To give you any advice would require a crystal ball as you haven't told us anything about the micro you're using, how it is connected and the code that you are using.

How do you know it is not an assembly error? What have you tried to solve your problem? If you want an immediate fix - I dare says you're the only person at this point in time that can effect such a thing. Rather than panic, why don't you apply a slow logic method to your problem - you'll have it fixed in hlaf the time!

some advice - test only one row first. Check the port pin levels and have your code print out the port information. Once you've got that confirmed, then try to debug all the rows. Then the debounce and so on. It is most likely a simple and very obvious problem and a 4*3 keypad is fairly simple.