Some of buttons on my remote are stuck and some of them just do not respond at all.

This is a very common problem for any remote control. The best way to solve this issue is to start by cleaning the remote from any dust or derbies. However, if that doesn't solve the problem use this guide Logitech Harmony 950 Troubleshooting to troubleshoot the buttons. After troubleshooting if the problem still occurs you can follow this guide to replace the circuit board or the keypad Logitech Harmony 950