my ethernet connection is not working

first of all i have windows 11, norton 360 & have combo router/modem.  also my wifi works just my ethernet connection does not work

around 1 week ago my ethernet connection wasn't working it now says "unidentified network" & in properties it says "no dhcp server was found" even though

in the "services" section of win 11 it says dhcp server is running.  I tried every single troubleshooting there is & the only one that worked was unplugging my 

router/modem which i did for 5-10 mins i plugged in back in & my ethernet network was working again but only for about 5 mins then it went back to "unidentified network".

 I think if i can get a replacement box that might cure the problem but if anyone else has had the same problem & can help i would appreciate it