My new (refurb) Sansa e260 is exhibiting this
same behavior. I received it in the mail, booted the OF to check that it worked, and promptly installed Rockbox. Rockbox worked fine for a few days. One night I fell asleep listening to music on it. When I woke up the next day, It was frozen at a blank (black) screen with the wheel lit up. I held POWER for 30 seconds to turn it off, then turned it back on, and it stayed stuck on the blank screen with wheel lit up.
I kept it in my pocket for the rest of the day, and at some point took it out and noticed it had turned itself off. I turned it on, and it worked. Rockbox booted up. I listened to about 1 and a half songs before it seemed to crash (music stopped, screen appeared frozen, I didn't see any error message like the expected "data abort"). On turning it off and on again, it resumed the "blank screen" state. Two more times over the next few days, I just left it alone, and it started working again, then broke again. It broke again about 2 weeks ago, and hasn't come back to life.
So I followed the instructions on SansaE200Unbrick for all of Recovery Mode, Manufacturing Mode, and Pre-boot Mode, but I get no feedback at all from the device (other than the fact that it turns on when connected to USB or pressing POWER). Nothing on the screen saying "Recovery mode", and no USB connectivity.
I'm thinking hardware problem, but the fact that it responds to holding POWER for 30 seconds gives me a little doubt.
EDIT: I also tried removing/replacing the battery with no difference in behavior. Also tried booting it with no battery (just off USB power), with the same behavior, except when connected to USB, it turns itself back on straight after turning off (the light turns off for a second, then goes back on).