Nothing at the stage of the 'problem', cause any startup program cannot get CPU allocated to it. Avast-setup is madly consuming all available cycles.
Managed to, eventually, start the system - took nearly 35 mins before I could get to the system to get the task manager.
One main task was Yahoo Messenger (dont ask). Removing this from the startup group did not solve the problem. Only other specific tasks are ctfmon, and Toshiba power-saver modules. Relatively clean machine; no malware, bots, etc.
Removing 4.8, as earlier, and reinstalling 4.7, the system worked fine.
Ive since reinstalled 4.8 from the full instal package, with the same symptoms.