It shouldn’t. it should reboot within minutes. Does it fully bootup after a reboot? Does it cycle? Does the ssid broadcast? What are the leds doing? 

It will come back on for about two minutes then cycle. Takes a few minutes to cycle then wifi for a few minutes then cycles. It does this for about 6 hours then it gives you more time between cycles (maybe 20 minutes). It does this for days. Probably takes about 4-5 days before it stops cycling.

I have a Linksys extender RE7000 purchased about 4 years ago,  but not able to connect.  Is it compatible with G20 ?  

when its up and running, get a screensnip of the cable connections page. One of my modem/router combo devices will cycle until get gets a good connection to the ISP. maybe yours has similar issues

G20 is compatible with all extenders. Some extenders will work with WPA2 mode.

If you experiencing issue while trying to setup, I would suggest contacting Extender’s manufacturer for further assistance.

​@SURFboard Moderator the users mikef thread jumped onto someone elses thread. I ignored their posts as they have their own thread we should be responding on so their info isn’t confused with the OP’s.