Cseries :: C2-01 Unable To Play Downloaded Video Content

I have a new C2-01. I know it is relatively basic in function but am sure that videos that are downloaded and installed to the device ought to work. I have looked into it as much as I can and it appears the Mpeg-4 or mp4 certainly should play on the device. I have managed to install an mp4 video and only get the audio of the video but no picture. How to get everything working - either which types of video format I need to use or whether a video player needs to be installed. I wish to use it on a monitor rather than the small phone screen via the av connection lead that nokia uses on many of its phones.