welcome to the forum.
what os and what version of avast you using?
it should work with the uninstall tool to remove avast, but why are you so sure it is avast that cousing this problem? not the wmp?
http://www.avast.com/en-se/uninstall-utility.
this is the tool you should use to uninstall avast.
do you have any screen shot where this two are conflicting with each other please post them so we could check in to them if there is something that have to be fixed from avast point of view.
good luck.