Long time Shutting down

Everyone knows that normally shutting down system is just about some seconds, just yesterday I noticed that my system is hanging up, and hard to shut down, so i just long press power button and I removed one of the RAM, it work fine, after some minutes it hang up again, letter I noticed one of the slot is at failut,

So the major problem is why the system is hanging and why it takes an hour shutting down?????