The letters E D C don't work

That only a row of keys does not work makes it sound that a trace for the keyboard is damaged or loose. Tho, it could also be way more complicated than that.

Have you ever spilled any liquid on your laptop, or gotten it wet? It may not necessarily be the keyboard per se, but could some motherboard components that has failed.

I did not find a full tear-down guide when making a quick check, but Lenovo has a dozen or so removal and repair videos for your specific model. You could open up your laptop, and re-seat the keyboard cables and see if that helps; as well as checking for any obvious component damage or corrosion. If that does not work you may replace the whole keyboard, but as said before I cannot guarantee that the it is the keyboard that is faulty, and not some motherboard component that has faulted.

If the unit is relatively new, you may be able to contact the retailer to have it turned in for repair.