Same thing happened to me. I also have installed powerdvd. I set the region of powerdvd with dvdgenie and it won't read a disc of a different region than the one specified on dvdgenie. This is perfectly natural but mpc seems to use this setting as well: if my powerdvd is set to region 4 and won't read r1 then mpc will read r4 and won't read r1.
I know it could sound crazy but since you don't have anything else installed it could be using the region of you windows media player. Change your location in Control panel and see if it works.
I know it could sound crazy but since you don't have anything else installed it could be using the region of you windows media player. Change your location in Control panel and see if it works.