dhcp issues. Home. No network...what is happening?!

Only my PC  (thankfully)loses its wireless internet connection from time to time but when it does, it is for months. When this happens, all of the other devices (Smart TV, Ps5, phones, laptops etc) remain connected. My PC will show connected but with no internet. When I run the various windows checkers they say they cannot reach the DHCP server. I do not have a network, but have multiple devices using the wifi on the gateway supplied by Xfinity. I have no other routers, just one gateway running everything wireless. I have no idea what I am doing.

I have looked at so many sites and done so many things over the last year, but nothing works. I have "flushed and reset" the IP, turned off the gateway, turned the PC off, etc. When I try to do anything recommended to access the DHCP server it says access denied and I am the only account on this PC.

Again this is just one PC and I am using the gateway/router/modem provided by Xfinity. I would just get a new one but nothing else is impacted, only this PC which leads me to believe it is something I did.

Two clues: It has randomly come back before when I connected an ethernet and left it connected for a few days and then removed it, but that does not always work. The second clue I got last week was that it was working fine, then I put in a window air conditioner on the same plug asthe PC (not the gateway).   Not sure if it is related or not.

My PC is sitting directly above the router in the room below.

Any help walking me through how to fix this would be helpful. Any chance I should just update/replace my Wireless adapter (card?) to something more powerful, is it the gateway or is it something else? The automated Xinfinity troubleshooter is NOT helpful. Again, I am a novice, have no idea what I am doing and do not have a network in this home as far as I know. 

Thank you so much, 

Kelly