I've been using Sygate Firewall 5.0 for about 6 months without any trouble but now for some reason it won't startup and when I try to manually load it says it cannot open. Should I try re-installing the program?

if you want to research the problem start with your application logs in your Event Logger... it can be found in the Control Panel under administrative tools... but un and reinstalling may be an easy fix

I've checked the log and it has an error saying that the registry doesn't have the necessary information or the DLL files are not present. If re-installing doesn't help, can I use system restore?

I had this same problem with an anti-virus program. One day it just stopped loading. A system restore did "fix" the problem.

Could be a virus!! Nimda and (the other name escapes me) are capable of disabling anti-virus and firewalls.....I've been a victim of these happenings.