Slow downloads with no router, only DSL modem

[Hikaruhime]

A few years ago, I used uTorrent with excellent speeds and no problems. We got a second computer in the house, and then had to hook my Windstream DSL modem up to a Linksys router. I could never got the port to forward correctly, so I had to live with the slow speeds and "closed" port. However, the second computer is now gone and it's just back to my own computer. Even though it is, once again, just hooked up to my DSL modem, I am still getting the red/yellow "closed" port signals and slow speeds. Sometimes I may get up to 150kb/s, sometimes as low as 5kb/s! Averages around 70kb/s. The number of seeds does not matter. The torrent I am downloading this moment has over 20,000 seeds (only 7 of which I can connect to) and an average speed of 30kb/s. Since I no longer have a router hooked up, I don't feel like I should have to deal with these slow speeds anymore!

So, my question is this: Why am I still getting the "closed" port signal even though the router is gone? Is there something I need to do to "undo" the port forwarding? I did have to go in after taking out the router and reset my computer to "automatically locate an IP" (internet wouldn't work otherwise) if that makes any difference. I'm not sure what information I should include, so if there's anything else, please let me know. I hope someone can help! D:

EDIT:

I selected "Enable DHT" and that seemed to solve the red signal problem as I now have the yellow signal instead, yet I have not seen an increase in speed. I did manage to see the green signal for all of 2 minutes before it reverted back to the yellow signal.

[Switeck]

http://www.portforward.com ROUTERS section lists both routers and modems that have NAT (router) features. Did you check to see if your modem was on their list?

What software firewalls (often included in antivirus/antispyware software) do you have?