You make sure that the files are supported on the specific mobile phone but if you see that the supported format do not play on it, there might be some error on the application and hence you should have it restored to factory settings to get the problem solved.
hey dude... its simple. sometimes the version is not specific relating the extension or the format of 3gp or mp4. I don't know abt mp4 but I have an ans for running the vid. thru 3gp format. istall "FREE 3GP VIDEO CONVERTER" AND DOWNLOAD THE VID INTO THE LAST OR THE GIVEN 4TH OPTION OF THE 3GP FORMAT.