This morning, I noticed I wasn’t able to access my PR4100. I see the flashing blue power light. No activity on the drives and they are all solid blue, and the fan is running. No other button works and I can even hard power it down cause the minute I press the button, without holding it down, it shuts down right away. Start it up again, it goes back to the same issue as I have described. Seems like it is stuck at an initialize stage, but I do see the “Welcome to WD My Cloud PR4100” on the LED but I can’t use any of the buttons to scroll through the LED messages either. Would greatly appreciate it if you have a solution to how to fix this. I’m really worried as I have so much data on the NAS. Thanks for any suggestions or solutions.
Thank you so much for the assistance. I’ll try that. Is there any specific process I have to follow or should I simply put in the firmware and start it up? I have owned this unit for many years and didn’t really have to do much other than swap out the faulty drives.
Hmm…interesting. I have done that inserted into the ports on the back of the unit. I have tried both ports and nothing seems to happen. I have extracted the files and copy this to the root of the USB drive. The interesting thing is, it start up right away and I see the welcome screen. Normally it would sort of initializing the startup before I even see the welcome message on the LED.
Yeah I know what you mean. Double checked and it seems to be FAT32. I find that my unit doesn’t shutdown. Normally when I press the power button for a few seconds, it will power it down completely but when I press the power button now, it just turns the unit off. When I press it again, it turns it back on right away (and doesn’t go through the usual initialization before startup). Maybe that’s why it is not booting up from the USB because it is not fully shut down?
Wow, I really appreciate the detailed instructions. Yes, the fan is running at full speed. Ok, I’ll try to find another USB stick. The one that I have is fairly old too 
Does the LED display show any kind of info other than Welcome to “WD My Cloud PR4100” when it is being booted up by the USB? Well, let me try another USB stick first and see. Fingers crossed.
I noticed you indicated putting the USB in the front slot, I put it in the back previously. Anyway, trying a new USB stick and putting it into the front port. Hopefully, something will happen. 
No luck. Still didn’t boot. 
