My Cloud is connected via cable to my router.
Sometimes it will appear under “Network”, - using File Explorer, and when it does I can right click it, select “Open” I can access my files without problem.
Sometimes though, it does NOT appear, and I cannot access my files.
I previously used a MAC, and had the same issue, but blamed my MAC.
Now however I have a new PC and the exact same problem continues.
The MyCloud is visible from Device Manager, and diagnostics tests etc. run OK.
Help me please! I’ve got loads of stuff stored on it!
Have you read this ?
What OS are you running?
Windows 10
Yes read loads before posting here.
Couple of suggestions. First is to assign the My Cloud a static IP, if you haven’t done so already, through your network router’s administration page.
Second, because you indicated you are using Windows 10, see the following link if you haven’t already and check/see if the suggestions in there help. In particular Windows 10 Specific Method 1 through 5.
https://community.wd.com/t/compilation-of-windows-10-methods-steps-and-solutions/142576
WOW! Randomly, it’s made itself available via explorer again! I think I might just create a backup of everything onto my PC, and then get another external hard drive. Assuming it stays visible/accessible long enough for me to do this. Thanks for your help everyone! 
Devices coming and going from a network are often a sign of IP address conflicts.
How is your network configured (i.e. how is the MyCloud connected to your router, and how is your Mac/PC connected to your router)? Wired ethernet? WiFi? Powerline adaptors? Firewalls?
What router are you using?
