When i start my sansa express mp3player sandisk appear & then it switched off automatically what will i do

There is a small hole at the rear side through which you can insert a small pin to press for 5 seconds to reset the device. try this on and reset. if not connect to a PC and open files for detecting any corrupt ones,and delete them. save only the scanned files back to the ipod. helpful? Good day

Check battery voltage or try reset