ELK-M1XEP not connecting to network

My connection from the M1G to my Indigo setup has been neglected for quite some time. 
I have been trying to get it up and running again this weekend, but I am having trouble with the  ELK-M1XEP.
I don't see its MAC address showing up on my router. 
I have power cycled it and plugged it in and out, but no dice. 
Is the thing dead or could there be something else going on? The thing is kinda pricey so I don't want to spring for another one if I don't have to. 

There is a known problem with M1XEPs suddenly losing their factory MAC address.   This was fixed in  XEP firmware level 2.0.42. If you're not at that level, that might be the cause of your problem.
 
Have you tried the Elk RP2 M1XEP Setup "Find" function to see if it sees any XEPs on your network?  The M1XEP standalone diagnostic program may also be helpful.
 
When the XEP loses its address, it often changes to 00409D:433597 or 00409D:BADBAD.  If you see either of those on your network, that's what happened.   You can't restore the original address without sending the XEP back to Elk.  But you can reconfigure your network to work with the corrupted address. The firmware fix only prevents the corruption of the MAC address in the first place.

One other thing to note is that older M1XEP firmware used TCP/IP SSL protocol. SSL had security issues and the world moved on to TLS protocol. The recent M1XEP firmware supports TLS, but dropped SSL. Windows 7 and later also have dropped support for SSL. You also need to use an updated version of RP2. I imagine this will have ripple effects with Indigo.

Thanks RAL
I don't see anything with the 00409D MAC series on my network. 
I'll take a shot at the other diagnostic stuff and get back to you. 

There is also this:
https://www.elkproducts.com/forums/topic/alert-m1xep-and-windows-compatibility-connectivity-issues-2/
 
Of course Elk shouldn't be blaming Microsoft for the failures of Elk itself.  It was not a decision that Microsoft made, it was a collective decision made by a browser forum to deprecate the use of 1024-bit keys.  That was also not done overnight, but was a phased approach with ample warning.
 
https://searchsecurity.techtarget.com/answer/From-1024-to-2048-bit-The-security-effect-of-encryption-key-length#:~:text=The%20Certificate%20Authority%2FBrowser%20Forum,by%20the%20end%20of%202013.
 
I guess something announced in 2013 was not enough time for Elk?
 
Nothing is stopping Elk from writing software that doesn't use binaries or capabilities in the OS.  They could write software that has OpenSSL or LibreSSL in it and they can support whatever they want, even SSL 3.0 or lower.