d,c,e, 3 sometimes do not work & sometimes they do

[Wyatt23]

some keys do not work someimes

 

[hang-the-9]

Those are all in a single row, sounds like a bad connection or bad keyboard. Reseat the keyboard, if that does not fix it, replace it.

 

[Shaun o]

The keyboard matrix bellow the keys is damaged.

You have a plus feed to each key, and a set of keys such as cde share a ground or return signal.
When you press a key down it creates a bridge to create a circuit loop.

Once it happens, if the keyboard is very cheap, as the other poster said simply buy a new one.