3 Software Firewalls = Bad
Norton = VERY BAD (Makes PC into a 486).
A Firewall Blocks Access but as you have opened up Ports / Pograms to allow it through - what is it Stopping?
To-Do
Check your PC and what you have Installed.
Remove All Firewalls Bar Built in one.
Questions
1.What Spec of Server?
2. What UPLOAD do you have (could not cvare less about your Download speed)
3. Do you run a Web Site on same machine?
4. Are you Grabbing Torrents at the same time?
5. Are you running Client on the same machine as server?
What is a DDOS?
http://en.wikipedia.org/wiki/Ddos#Distributed_attack
Maybe learn about Computers and Comms - this may help instead of installing as many Firewalls as possible without understanding any of the process.