There is a dental cavity in your molar which has caused the tooth to break down.Since you can't give pressure on it,that means there is discomfort while eating on that tooth.
So probably you have a deep cavity involving the pulp of the tooth leading to a dental infection.
Next Steps
Please go for a dental check up and a dental X-ray if required.
Health Tips
Please don't ignore the tooth because it's not paining you right now.The fact that you can't eat with it is proof of enough damage to it.Get treatment soon.