Bittorrent no incoming connections?

Well, for the last three or four torrents I've tried to download, there were between 39 and 500 possible seeders, (in the parenthesis), but I cannot seem to get any seeds nor activity. I can, however, upload and download torrent's I've already used; the one torrent that is downloading has slowed to a crawl though. It has dropped to between .1 and 2kb/s, down from 138+, and the number of seeders has remained constant. This is when I started getting red and orange symbols next to my total download speed, and it is now sitting on the orange 'no incoming connections'. It's been like this for a few days now, and it is POSSIBLE that the router was changed, but I didn't notice anyone messing with it. I don't want to bring this up with the parents however, as the techie that maintains the local network, (the daddy), has an agenda about p2p sharing, (my sister has managed to bring down her comp and almost infect the entire server several times through her lack of being computer savvy. (it's savvy, not sawy)), and I imagine I'd just be walking up to be chewed up and ignored in a patronizing way. Anywho, the port it currently uses in pref/connections is 57426, and first that's an awfully high number from what I've just read. Second, would opening an extra port in the firewall and setting bittorrent to use it, (lets say 6881), fix the problem or not? I think I've got a NAT system because we have 5 computers in the house that all share the same cable connection, but I'm no expert in hardware and therefore I really don't have a clue. Input?