I don't think this is confidential information about Apple products but a Parallels issue. I had the same problem of a black screen after installing the beta pack from the App Store. The reason for installing Mac OS X on a virtual machine is exactly to test this kind of beta software instead of installing it on the main system.
Yes,maybe you are right. I'm just new at betatesting with Apple and I don't want to mess up things. Anyway, I noticed that the system IS working, just the display is black. If I use screen sharing from my real Mac to access the virtual machine, I can reach the desktop.
I tried with the uninstaller on the Parallels Tools ISO but it doesn't work. I will start again with a clean VM.
Correct. but then you'll be stuck with if want to share files/folders No.. If it can't boot, you are unable to uninstall Parallels Tools.. you must start up a new VM from scratch.