after harvesting URLS and clicking "PR" in the top right. nothing at all happens.

Any ideas as to why? I JUST got this tool.

Make sure that you have the latest version and then contact customer support

Well, you just can't press the PR buttom. First you have to run the PR checker, it's in the menu to the right (Check Pagerank) and choose either URL or domain. After that's done, you can click the PR buttom and it will show you the sites with high PR at the top.