How to check if my network card is working debian

About 6 weeks ago I setup a little server for my daughter and I to play minecraft. I had trouble initially getting it to connect to my xfinity router, but it eventually connected (disconnecting cables, restarting router or server). After that it was rock solid and we have put probably 50 hours of play on it over a month. Then we had a power outage and my NAS box disconnected, so I turned everything off and back on. The NAS is working fine now, but the server will not connect. I have turned everything off and on about 10 times, tried different cables, different ports. Nothing. I do have it set to a static IP inside the xfinity router. Is there a way for me to rule out hardware damage to the server? I am brand new to this and literally need copy and paste commands to get stuff to work. I have the server hooked back up to a monitor and it is connected via ethernet to the router, but they aren’t talking. The little lights on the back of the server blink. Any suggest on where to start?