Your problem may be due to the logging carried out by the Firewall.
The easiest way around this is to make the log file itself read only - a useful discovery by Soya.
Log Files usually at: C:\Documents and Settings\All Users.WINDOWS\Application Data\Comodo\Personal Firewall\Logs
Right click the file and make it read only. This drastically reduces the drain on your system in most cases. Worked for me and many others.
