Assuming this is a single bay My Cloud and not a My Cloud Home. As a troubleshooting step, try performing a 40 second reset.
How to Reset a My Cloud (single bay) Device
Try to access the My Cloud Dashboard.
Sometimes the front LED dies or the blue color dies, does the front LED show any other colors when power is applied to the My Cloud. Does the back LEDs of the network port on the My Cloud light up?
Other troubleshooting steps. Try a different Ethernet cable to connect the My Cloud to the network router. Try a different networking port on the router. If you have a computer with an Ethernet port, connect the My Cloud directly to the Computer using the Ethernet cable. Put a network switch, if one has one available, in between the router and the My Cloud.
Hard drives can and do fail, so it shouldn’t come as a surprise if one has had the My Cloud for a number of years that the hard drive within it might fail. If all other troubleshooting steps fail to resolve the issue one could extract (or “shuck”) the My Cloud hard drive from it’s enclosure and, using a USB to SATA adapter (or similar method), connect it to a computer running Linux or that uses a Linux driver and attempt to read the contents of the My Cloud drive. If the drive is readable then one can copy the user data off the drive to another location. There are a number of videos on Youtube that show how to shuck/extract the single bay My Cloud hard drive.