hello, I am having difficulty listening to P4 lectures on Futures.

hello, I am having difficulty listening to P4 lectures on Futures. I have been listening to P4 lectures on my laptop but suddenly I can no longer hear the audio explanation but it will be playing.I tried playing other videos from other sites on my laptop and i plays with the audio.my speakers are all ok but i cannot hear the voice while trying to play videos of the lectures. Help out