Song plays only for 10 seconds

Hello,

I have got a mp4(name of company:FIRST1). I gave it to my sister to listen song. But, when she returned it to me each song played only 10 seconds.
Besides that, when i plug my mp4 to computer via data cable. Some time it shows its icon and some time not.
These are my due problems.
Please can any one help me
I would be obliged if some one is trying to help me,
Thank you!