Various internet reports seem to send very mixed messages about Zone Alarm Security Suite. Some people seem very happy with it, others say that it slows down their computer substantially.
And some say it uninstalls cleanly, others that it doesn't.
So it's difficult to know exactly where your problem lies. But here's what I would try.
Uninstall any Zone Alarm products in your computer.
Run CCleaner (click here), including its registry cleaning module.
Reinstall ZA Firewall Free - or choose another free firewall, such as Comodo (click here)