Samsung C6625(wm system sp2006) failed to answer and hang up keys.

Dr. Xu, this is the reason for the confusion of shortcut keys, which may be related to your setting of shortcut keys.

You can try to reset the system by using Start-System Tools-Master Reset. Of course, remember to back up your contacts and text messages before restoring the system. There is a software backup of smart phone Studio online, which is very easy to use. You can try. Good luck!