I've been trying to fix this problem myself for a few days. At some point my .rar file association got changed to use explorer.exe, now no matter what method I try I can't change it to use 7zip instead. This is a problem because any time I click a .rar file explorer keeps trying to open it over and over again and stacks up hundreds and hundreds of copies of the explorer process and I can't get it to stop unless I delete or move the file, which is impossible when it's trying to open. I've tried using the 'open with' option, going through the control panel, and even changing the association in the registry but it absolutely refuses to change even after a restart. Any help would be much appreciated.