- power off (not sleep) the devices trying to connect
- disconnect the router from the modem
- power off the modem
- factory reset the router (usually hold reset button in for 5 seconds)
- once it's done resetting, power it off
- power on modem
- once it's full up reconnect router and power up
- once the router is hot power on a device and try it
Edit: when you directly connect it, are you moving the pc cable to the modem (from the router) or using the cable coming out from the router and directly to the pc? Want to eliminate cable issue. Do wifi devices work?