Be sure you are using the power adapter that came with the router. Same with the modem. If you have issues with multiple routers then I would suspect the cable, the modem or the ISP. Connect a PC direct to the modem via an Ethernet cable bypassing the router. Be sure to use a good Ethernet cable. Note that we had a poster report that the cable that came with the router was bad, so even if it is new does not mean it is good. Power cycle the modem and PC. Do extensive testing to see if it fails. If it fails, review the modem logs (if any) or you may need to contact your ISP. If it works, reattach the router and power cycle the modem, router, and PC. If it fails, give us more detailed info of the issue.