Pull the xamarininstaller.exe local from the downloads section. Double click it to give it a go. Confirm dialog for "automatically send troubleshooting information and usage statistics to help improve this software" comes up. Leave checked and hit [continue]. User account control comes up asking if I wish to allow this program to make changes comes up, I click "yes". Then nothing happens. Nothing stuck in task manager, et al.
Run as admin gets roughly the same effect without the UAC.
I can get to the individual products fine, but thought I'd hang this out there.
Healy in Tampa