Have you spilled any liquid at all on the keyboard or upper case?
Here is a link to the service manual for your laptop (at least I think it is your model) which shows how to dis-assemble the laptop. This will allow you to remove the upper case of which the keyboard (and also the touch pad) is a part.
You can cause more problems than what it is worth if you attempt to repair a keyboard so it is preferable to replace it. On p.62-63 of the manual there is a list of the part numbers for the upper case assembly applicable to your particular model variant.
Unfortunately for you the replacement part is not cheap. Just search online, using just the applicable part number in the search box, (do not add Lenovo or keyboard etc. - it will skew the results) for suppliers of the part.