Windows 7 Home (all current update).
Advast 2015 Anti Virus and Firewall ver. 10.4.2233
If I disable the firewall start SmartWare the MY Cloud is displayed.
I restart the firewall and close/rerstart SmartWare the My Cloud is Displated Until the next Reboot.
It appears that My Cloud is doing the back ups after the system restart.
Is your My Cloud connected to your router? Does it have a static IP address? The next time this happens try turning off your router and then restarting it. After that check to see if the My Cloud shows up.
Unless your IP is static each reboot may change the address.