Vlk, many thanks,that's almost certainly it - will post back if it (or one of the thread suggestions) doesn't work but I imagine it will (not an essential tweak, anyway). Thanks too Tech and DavidR - and sorry about not picking up the previous thread. I hadn't picked this up earlier.
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Bill
There is a lot if information on the forums and it can be difficult to find when you aren't sure what to search for, this particular problem would just seem so strange and not associated with the reboot requests, making it even harder to find.
What might help for the future when using the forum search tool, there is an Advanced Search option, which is really useful as you can order the results in a most recent first. This is most likely to return 'current' problems people have and may be more likely to return more relevant information.
The main thing is to get the problem sorted and hopefully you will.
Welcome back to the avast family.