Greetings!
One of the issues I have seen pop-up repeatedly on these fora is the “Oh no! I can’t find my [insert name of device here]!!!”
Though I cannot guarantee that there won’t be other reasons, I suspect that, at least in some cases, the device is attached using a dynamic IP address, (DHCP) instead of a static IP address. Obviously, if you know what you’re doing, setting a static IP address is the desirable thing to do. (And if there is enough interest, I’ll post a “How-To” on that topic.)
Assuming that either you have a dynamic IP, (i.e. the network address can, and often will, change), or a static, (unchanging), IP address and have forgotten it, there is a way to find out what’s happening.
There is a cute, freeware, utility for Windows devices called “Advanced IP Scanner” (located at http://www.advanced-ip-scanner.com, that will allow you to scan your network and discover what devices are on your network, and where, (at what IP address) they are located.
I have been using this a lot, both on my own network(s), and the networks of the clients whose systems I care for.
With this utility you can scan your network and discover everything that is currently connected to it.
This is useful because:
- It gives you a listing of everything it can find on your network - both IP and MAC address.
- Knowing what is on your network is a Good Idea, just in case someone (or something!), you don’t know about is secretly snagging a ride on your wireless or hard-wired network.
Hopefully this will help some of the people who discover that they cannot connect to their devices anymore.
Jim (JR)
Mine has been running now for 4 years non-stop on the shelf plus its USB sibling a 3TB USB drive for safepoints, despite numerous power cuts (house improvements), 2 routers breakdown and still churning away. Actually, I have no idea what firmware is running until I came to this forum and saw the release notes then I checked that it is running the latest. so it auto updated itself several times over the years and kept going, amazing. (Of course all files are there, including safepoints, sync folders etc). 
Impressive.