They did not realize that McAfee was installed and installed Avast also.
hmmm....and Your topic title say AVG ... ???

well… can you start in safe mode? … if so try uninstall from safe mode

if success …then you need to run removal Tools for all AV removed so that all leftover files that may conflict is gone
Tools found her http://singularlabs.com/uninstallers/security-software/