Hello there and welcome to the community. 
The fix for the black screen issue is simply to use the end task tool on WeMod via the task manager. You shouldn’t have to re-install. Could’ve used the search button here on the forum to find that solution, but never mind. 
Your download issue is commonly caused by interference from an antivirus program (Windows Defender is still an antivirus).
First of all, please make sure your Windows Defender signature library is up to date. Even if the Defender software itself is up to date it doesn’t mean the signature library is. Here’s how to do that: https://support.microsoft.com/en-gb/help/4027712/windows-10-update-windows-security-signatures
If that doesn’t resolve your issue, give the troubleshooting steps in this post a go: Can’t Install WeMod