Long story I'll try to summarize:
1. My old router (not Comcast hardware) died recently
2. I reverted to connecting directly to the Comcast modem
3. Everything could connect (phone, tablet, switch, printer) except for my desktop, which lost connection after a day or so
4. Bought a new third party router, desktop worked for like an hour before dropping (all other devices are fine)
5. Returned router, traded old Comcast modem in for a new one (since I was overdue to do so)
6. Got the new modem set up, desktop worked for like an hour before dropping (all other devices are fine)
So this is where I am now:
• I can connect all my other devices wirelessly to my home network direct off the Comcast router.
• I cannot connect my desktop, either via wired ethernet connection or via a wireless USB dongle.
• I can connect my desktop to an "xfinitywifi" hotspot in my apartment complex via the same dongle, so my desktop has some internet connectivity at least (but not to the "xfinity" hotspot, or, as mentioned to my home network from my Comcast modem)
I've installed the xfinity xfi app but I cant troubleshoot devices that the app can't access. And no, the desktop isn't paused either.
I have tried resetting the gateway multiple times, but the result is the same, everything but the desktop can connect.
I've also tried some options suggested elsewhere, like removing and re-adding my wireless adapters. Nothing works.
When I try to connect to my home network via wireless it asks me for a password, which I provide (the password is definitely correct, I use it on every other device) and then it simply says "Windows was unable to connect to [my network name]" and that's it. The Windows (7) troubleshooter doesn't help.
So my only remaining thought is that my desktop PC is somehow blocked from my home network? But I don't see anything obvious to that effect when accessing 10.0.0.1 from one of my other devices. And I have no idea how it would have gotten blocked... I've used this PC on this connection for years.