How to free memory in WPF [on hold]

I have implemented WMP in my WPF app. It plays .mp4 file for me. My target system is Win XP with low configuration. I play .mp4 videos repeatedly on app. It works as I expected but after some time it stops working and black screen appears. I know its the problem of freeing WMP object from memory. Here in my case WMP object goes out of CLR scope that's why CLR is not able to free its object and memory dumps. Can you guys please give me some suggestion to release this object from memory so my app doesn't stop and works well. Thank you.