Make sure you have the latest MPD version (via mpd --version, not mpc version). All the time, bugs are found and fixed, and your problem might be a bug that is fixed already. Do not ask for help unless you have the latest MPD version. The most common excuse is when your distribution ships an old MPD version - in that case, please ask your distribution for help, and not the MPD project.
Check the log file. Configure '
verbose"' or pass
Sometimes, it is helpful to run MPD in a terminal and follow what happens. This is how to do it:
mpd --stdout --no-daemon --verbose