I read that you clicked Reset for Internet Explorer, but it's specifically the cache you need to clear and I'm not sure reset does that. To do this, go into Internet Explorer (even though it's not your primary browser) and then go into "Internet Options" and on the first "General" tab, click to delete "Browsing history". Specifically make sure "Temporary Internet files and website files" is checked and make sure that "Preserve Favourites website data" is NOT checked.

After doing that the launcher should open as expected (the launcher basically is an Internet Explorer browser hence why you need to clear the cache there, even if it's not your main browser).