Hi Christopher
possibly a silly question, but have you tried turning everything off, then rebooting everything in the sequence of modem first, then the router, then the PC?
In each case allow the equipment time to 'settle down' before booting up the next in the sequence - usually at least 30 seconds.
You saying that the modem & router works with the laptop seems to suggest that it isn't a problem with the connection, per se, but the PC may just need to be 'properly introduced' again ?