Actually this is the results of being infected with different viruses. These programs protect themselves by denying any known applications from being installed that will locate and remove them. This is why it is so important to install antivirus programs as soon as possible.

About the only option you have left is to try to install the antivirus during safe mode and running it from within safe mode to clean your system.
If that is not possible then you must reformat and reinstall your system to rid yourself of the problems.

To enter safe mode:
restart your computer and immediately start toggling the F8 key until the start up page opens. Choose to start your computer into safemode. this may take awhile. You will have successfully entered safe mode if your desktop is shown with safe mode shown in the corners.