I have the same problem with my new Clip+ (no problem with a previous one).
Sometime, it reboots. sometime not. This time, he seems to be dead. No sign of life when i plug it.
If it wake up, i will try a new manual update (done recently after purchase).
You should not have problems like this with a brand new unit. You paid for a unit that works. Yours doesn’t. You did not get what you paid for. Return it.
This appears to be a firmware issue. I had the same issue and found the answer on a forum somewhere.
Go to Settings-system settings- Backlight. If the backlight setting is at 10 seconds this causes the lock button issue. Just select the next time level (15 seconds) or better and remember to save the setting when asked.
This resolved the issue for me. I hope it does for you.