OSX app store update (iMovie): "less than a minute" lasts more than five hours.

My iMovie update in the OSX app store is showing "installing - less than a minute" for more than five hours now.

Several other updates (that are more important to me) are queued up behind it.

What to do now? Can I stop the upgrade and is that a good idea? Can I see a log somewhere to determine if it is

still doing something?

Yes, this is an old computer (late 2009) but it still installs any third party software in a matter of minutes. Five hours just seems absurd.