Why is Sourcetree taking 10+ minutes to open and then won't even work when it opens?

[Bryce Messer]

When I open Sourcetree, the blue 'Sourcetree' image pops up for ~1 second, and then disappears - the .exe process continues to run in the background, though, and it eventually opens ~10-20 minutes later. However, when it opens, it doesn't work properly - it just stalls and freezes and I can barely click on anything. This issue started when I was using a rev in 2.#.#, but I uninstalled that, then installed 3.0.8, and the same issue has not gone away... Please help.