Hidden Firewall Issues

I’m using a DSL ISP, and Windows XP. I’ve been having issues with a lot of downloads, programs and games lately where the internet goes haywire and decides to quit or stop working. As well as many other issues. Everything I read points to a firewall issue. I’ve disabled Windows Firewall and I’ve also taken the time to skip my router which has a built in firewall. When I run programs they tell me I still have a firewall up. Is there a way I can trace where this firewall is coming from? Could it possibly be hidden on my PC, or could the ISP be putting one on for me without me knowing?