Sandisk Sansa Clip has ffrozen

I was just changing the music on my wifes Sandisk Sansa Clip when it froze up completely and now none of the buttons work and cannot turn it off any advice appreciated.Thanks

On the L/H  side is the volume control and the USB socket is that correct and the power button is the reste button ?

On the screen it shows it is transfering music from my PC to the Sansa and it seems to have got stock in the middle of the transfer and it says Writing in orange.What would happen if the battery goes flat as I am unable to turn it off.