SO after a quick search I couldn’t find the solution to my problem. I’ve downloaded and tried to install Sourcetree but I can’t get past the sign in stage. I’ve created an account and I get a license if I use the go to webpage button, but can’t continue after that. If I try to sign in using the sign in button, the window just comes up blank.
I ran into the same issue that you were having and I have managed to find a solution to it. Open up your internet explorer and click the cog in the upper right corner and select ‘Internet Options’. Next click the Security tab, followed by selecting trusted sites and clicking the ‘Sites’ button. This will open a new window, in this window add the following link to trusted sites https://id.atlassian.com/.
While this may not be the solution for everyone it did end up doing the trick for me, so hopefully it will help someone else out too 
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