There are several reasons why your car brake pedal is hard. most common would be a lack of vacuum pressure, issues with your valves or an issue on the pedal ratio. You might want to check those areas for possible repair. However, there are other reasons why your brake pedal is hard which can be identified when you had your car thoroughly checked. I think its best to bring your car to your trusted car shop to have it diagnose for possible repair. Doing this will fix the problem accordingly as well as avoid worsening the problem. Hope this helps!