I would recommend reinstalling/updating Comodo Internet Security (CIS) to the newest version by following the steps below whether you've had problems or not. This will likely avoid most problems you could otherwise encounter.
Before you continue with any of the following advice make a system restore point. This way if something goes wrong, which although unlikely is possible, you can easily recover.
Also, if you want to maintain your previous configuration after reinstalling you should export you current configuration before continuing to the following steps. This can then be imported after re-installation. However, note that sometimes the old configuration can cause problems after being re-added.
Section A: Always Follow These Steps (in order)
1. Disable Any Other Security Products You May Have Running
Uninstalling is usually not necessary, but if you believe that the other security software may be interfering, even when disabled, uninstalling may be a good idea.
2. Download All Software Needed For Removal Process
Users who are using a 32 bit operating system should download Revo Uninstaller Free from this page. This will not work for CIS on 64 bit operating systems.
Those running Windows 8.0 or 8.1 should also download this removal tool this link.
Those running Windows XP, Windows Vista, or Windows 7 should also download that removal tool. However, in addition they should download an additional removal tool from this page. Those running Windows 8 or 8.1 should not use this tool as it may cause damage to that operating system. However, it is safe for all others.
3. Uninstall Comodo Internet Security/Comodo Firewall (CIS/CF)
Advice For people with 32 bit systems
Those users running a 32 bit operating system should start Revo Uninstaller Free. Revo will make sure that almost every file from your previous version was removed before you install the new version. Just start Revo and wait until Comodo Internet Security (or Firewall/antivirus, depending on which variation you have installed) is listed. Note that for x64 machines Revo will not locate CIS. You should go to the next paragraph for instructions on what to do. Otherwise, in Revo, choose to uninstall CIS using the moderate search option. Revo will first uninstall it normally using the builit-in CIS uninstaller. When the CIS uninstaller finishes it will prompt you to reboot, but select no and let Revo complete its process. It will then search for, and find, most files/entries that are left over. I would recommend that you delete all. After this restart your system.
Advice For people with 64 bit systems
If you are running a 64 bit operating system Revo Uninstaller Free will not work. Thus, you should uninstall CIS through the "add/remove programs" in the control panel. Just let it finish and, when it prompts, allow it to restart your system.
4. Clean Up Any Remnants Left of CIS/CF
Once CIS/CF is uninstalled, or at least removed as much as possible, make a restore point as a precaution, then restart the computer into Safe Mode with networking. Instructions for how to do that can be found here.
Then those users running Windows XP, Windows Vista, or Windows 7 should run the extra removal tool which you were asked to download through section 2. To remove remants select "Uninstall Comodo Internet Security" from the options. Then allow it to remove any remnants it can find. Once it is done you can safely close the window. Then also run the other removal tool downloaded, and follow the steps in the following paragraph.
All users, including those running Windows 8, should now run the removal tool, which is safe for all versions of Windows, to remove any leftovers from Comodo Internet Security. After opening this application first run step 1, which attempts to kill any remaining processes from Comodo Internet Security. Then, once that is done, you should run step 2, which removes any remaining files and folders. Note that there are other options provided, but that I would strongly advise that you do not use them. Only the first two are meant to remove Comodo Internet Security. The rest are for system maintenance and sometimes may cause serious problems with your computer if run.
After following the above steps you should restart your computer.
5.Clean Any Remnants Left From Former Security Products
If you ever had a different security program installed before you tried uninstalling CIS, then part of the problem could be due to interference from their leftover files. To ensure that this will not cause a problem please run the removal tool for each of those security programs that you used to have installed. A list of uninstallers for common antivirus software, can be found on this page. Please select the ones for any security programs you previously had installed and run them.
6. Now Install Comodo Internet Security
Download the latest version of Comodo Internet Security from this page and install it. Everything should now hopefully go flawlessly and