If 'I disconnected the video' means you have been accessing the VDI by RDP, then you will have a problem with Activate. When you disconnect RDP, the desktop of the VDI is destroyed but the machine (and BP) is still running. This means a process wanting to use Activate (or screenshots or click) will have problems, because the desktop is not there. Confusingly, when you reconnect RDP to investigate, the desktop is remade (like the light inside the fridge).
If you must use RDP (and it's not recommended) then you should log the VDI out and back in again using Login Agent.
See https://portal.blueprism.com/documents/v6-data-sheet-remote-access-tools