The hard-line connection to the internet is stable to my desktop computer.

If I turn on the wifi network the green lights persist (and the green wifi light comes on) but very shortly thereafter the internet drops if any wireless device connects.  The lights stay on, but even my desktop computer loses the internet connection.  I can restore the connection by resetting the router, but I've got to make sure nothing connects to the wifi unless I want a repeat drop.

Have tried a factory reset.  Have tried all the standard on/off tricks (unplug it all for 5m, factory reset, etc).  Pretty sure it's not my ISP because, as previously stated, the router works fine unless the wireless is turned on and something connects.

No VPN on the router, desktop, or anything connecting to it.  Windows 10 and Bitdefender, and I've tried turning the firewalls off but no dice.

When I first got the router a  few months ago it worked fine, but in the last couple of weeks I basically can't keep the wifi up.

Any ideas?