Keeps playing first few seconds of music files

Start by taking the battery out and reinstalling it.

If this doesn't work, and the keyboard is still responding, use the "soft reset" code - *#7370# - you will need to enter the phonecode (12345 if you have never changed it).

If that doesn't work, then use the "hard reset" code *#7870# - but be aware that this will delete all data that's stored in the phone memory - the contents of the memory card are not affected, however.

Finally, there is the phone reformat, which will also erase all the settings and data on your phone - to do this, remove the battery, reinstall it and hold down the "*", "3" and "Answer (green phone)" buttons and while holding them down press the power button. Hold the keys down until the phone starts asking the startup questions again. Having 3 hands helps for this proceedure.

If this doesn't help, then the last thing to try is to reinstall the phone firmware using the Nokia software update service - http://europe.nokia.com/get-support-and-software/download-software/device-software-update

If it still doesn't work after that, then about the only option is to take it to a Nokia service centre and get them to fix it, since it sounds like a hardware problem.