Some of my keys stopped working, yet if I press

First have the keyboard connector checked.
If it is loose or broken you may be forcing the connection by pressing down on the left center under the keyboard.(Secure or Replace)
Broken/damaged circuit can have the same affect. It could be as simple as securing a loose connection or a drop of solder in the right spot.

Broken circuit board different matter. Determine if replacing the keyboard will resolve the issue first. This may save you money in the long run. If the circuit board is broken and part of the main board. (99.9% chance it is) This will be expensive.

Make sure the keyboard is positioned correctly and the frame is not warped.

Without saying, do the simple checks first. May save time and money! :)

Hope this helps.
Good luck!

try to unplug and replug your keyboard cable, also if you can, try n check your keyboard on some other computer, if same thing happens ther also, they YES my dear, TIME TO BUY A NEW KEYBOARD :)

You have an "open circuit" somewhere inside your keyboard - it could be a bad solder connection or a broken wire. In either case I would recommend a new keyboard.