So the only difference from when it worked and now when it doesn't work is the modem and ISP?

Have you checked with you ISP? I can't think of anything else but something at their side or the modem. Maybe some firewall setting. Though I also think it's really strange it's just for the wlan adapters. Maybe if you tell us what they say,we might be able to figure it out(since I doubt the support can, they rarely do any good. :evil: )