We really can’t tell you that remotely, I’m afraid. Now that you’ve got the HDD out of the case, go for the recovery methods Bennor pointed to. If you can get to the data, the HDD is okay, and the problem lies elsewhere.
Have you checked the router (reset, try different router port, try different cable)?
Have you checked the MyCloud’s IP address hasn’t been changed by your router?
Have you tried a 4-second, or 40-second reset?
What were the ethernet port LEDs doing before you opened the case?
Have you changed your ISP/router to AT&T Uverse?
I’d have done all of these before cracking the case.
