in IE in a new account, the problem points to a corrupted Flash Plugin install.

Even though you say you don't want other browsers on your machine, the 'quick' test would be to do that; install another browser, go to IMDB.com using that browser and let it install the plugin, see if the trailers work. Then if you want to, uninstall that other browser.

Your options then are;

1] Use Adobe's own Flash Uninstaller to completely remove Flash from the machine, (at least, from this affected account). Reboot afterwards. That's important as it updates the registry to remove any Adobe Flash remnant keys and values. Then re-visit Adobe to install Flash.

I know you said you have tried all this, but did you reboot between the uninstall and re-install? It often makes a difference.

2] If that fails, Reset IE back to default. IE Tools > Internet Options > Advanced tab, then the Reset button.

Beware, doing this may lose all your Favorites, Home Page, History, Cookies, and any web site login details stored in IE. You can export Favorites beforehand and re-import afterwards, but not the other things.

Why do that? It returns IE to default state, no plugins, no add-ons, no toolbars. Then you start again with IE.

See if either of those work.

Mark