..."i can't uninstall MSE, because my uncle told me to have two antiviruses. i believe MSE and avast are compatible, as long as i don't get a bluescreen i won't remove MSE. MSE "locked" the system files, even when i tried to install a third-party theme, the system files won't change."
Sorry, running two resident a/v programs can cause an issue of system locks, so your beloved uncle is wrong. Not normal operating system operation, as you should be free to modify or change files within your operating system (which, btw, is not recommended) or install your third-party theme without issue (unless it was detected as malicious.) Even then, it could be clashing a/v conflict that caused your issue and your downloaded file was actually clean. See below.
Here’s what I recommend: Uninstall either a/v (doesn’t matter, your choice made freely, unless you do not own this system) and use this site to enable removal of either one: http://singularlabs.com/uninstallers/security-software/ Download the removal tool first that applies.
First try to uninstall either in normal admin mode using either Add or Remove (XP) or Programs and Features (Vista and later). Reboot when successful.
If you cannot remove MSE in normal mode, you must uninstall it in Safe Mode first. Caution: Your a/v’s do not run in Safe Mode (they are not actively protecting) so go offline to ensure you have no problems. You should be able to remove either using the tools provided after uninstalling first, except avast! aswclear.exe requires you be in Safe Mode to run this finalized executable. http://www.avast.com/uninstall-utility Uninstall avast! normally in normal admin mode, then go to safe mode to finalize removal using aswclear.exe. Reboot.
Running two antiviruses revealed the symptoms you were seeing when you tried to install your third-party program. Did you get a system lock when you attempted this? If so, classic symptoms of two a/v’s trying to scan the same file at the same time. One will not yield to the other, so the system effectively locks up.
You will wind up with less protection running two active resident a/v’s at the same time, not what would be, intuitively, more protection due to the clashing of a/v’s. It is their nature to scan all files that run on your system at the moment they run.
Even just uninstalling one a/v is not enough to remove all drivers specific to that a/v program, as these left-over drive(r)s will continue to run at the deepest levels of the operating system; these drivers can/will affect the remaining program left as the resident a/v, and thus adversely impact protection against malware that enters your system. I know you don’t want to risk the chance of lessening of protection happening to you.
That is why you use the clean-up tool of your choice. Reboot.
[EDIT:] Fixed typo.
[EDIT:2] If you are running Windows 8, then all you can do is turn off MSE (Windows Defender). MSE can be uninstalled from XP to Windows 7, but not from Windows 8.
