Downlaods Stop Abruptly, Require Constant Restarting to Fin.

[JOSfiwER234]

Some downloads stop abruptly and don't start again for minutes or hours. There are still lots of seeds, and it will seed from my end, but not download normally. I tried disabling 'randomize incoming ports', but that didn't work. Only thing that worked was to close Deluge and restart about a dozen times till it finished (this was a small torrent, but it also happened to larger ones). It would start up again for about 10 seconds, then stop again.

I'm connected directly to the modem (no router). I checked the FAQ, but I couldn't find how to "Check that local machine firewall or router is not detecting a SYN flood and blocking packets," on Windows Firewall. I'm using Windows 7.