When the file starts playing, click pause, try right clicking on the file name on the RHS of the view window in MP9, then click properties, if you are short any codecs, it should say there.
Otherwise, have you got the driver cd for the laptop, or have you changed any of the hardware in there. Goto control panel, click system, click device manager, check for any hardware problems.
Hope you can sort it mate. Luckily it's a laptop, so you can take it with u to ask someone who mught know...