I am experiencing some of your problems with my 18 month old Clip Sport. My problems seem to occur whenever I turn off the player manually with the On/Off/Select button.
I can usually manage to get my Clip Sport started by pressing down on the On/Off/Select button for ~20 secs and then let go. Then it displays the normal SanDisk start up logo. (Start-up does not occur if I keep pressing the button.)
My player functions almost normally when I allow it to turn itself off using the Power Saver feature (5 min of inactivity), or when I use the Sleep feature. These settings are available in the Settings -> System Settings menu.
