Problem playing full-length

Hey,

I have a show that I downloaded (about 150mb) and it won’t play the full length. it only says about 1 min and 10 seconds and if i run it, it only plays through the min and 10 sec, yet when i skip around (say 3/4 of the length of the bar that u use to skip around), it takes me to 3/4 of the way through th emovie and only plays another 1 min and 10 sec.

help!

thanks