Gawd, what a carry on. Before the two posted recommendations above appeared (thanks btw) I found some instructions to remove the Great Deal thingy.
1st instruction was to open programs and uninstall anything that one didn't recognise or was suspicious looking. I found something called YAC, Brazillian I think it was. So I thought, as I'm here, I'll uninstall that as I was pretty sure it shouldn't be there. Clicked uninstall and a window opened. The program looked like an anti-virus program which I didn't recognise and didn't install.
Started to uninstall, it reached 5% and went no further. Buggah, I'm thinking now this is a piece of malware in itself disguised as anti-malware and won't uninstall itself. I couldn't quit and close the window. I couldn't get anywhere so pulled the plug, so to speak. Upon restart, the machine was hopeless, couldn't do anything.
So forced it to start in Safe Mode which was ok. I had recently created a restore point so decided, rightly or wrongly, to revert to it (not something I had done before so I was a bit anxious). Well, it worked and the machine seemed to be behaving reasonably but YAC was still there. That wasn't the main concern as the whole point was getting rid of the Great Deal thing.
I downloaded "Superantispyware", ran it and it picked up YAC and other items, deleted that and I haven't had the GD popup appear yet either, so perhaps sorted. Stuff running quite smoothly.
I decided to create a new restore point and I got the following message:
"The Volume Shadow Copy service used by System Restore is not working."
Web search tells me to run System File Checker (sfc /scannow). I can't open the CMD window as administrator! error:
"The service cannot be started, either because it is disabled or because it has no enabled devices associated with it".
So I can't open Command Prompt to try and get The Volume Shadow Copy service used by System Restore working again...
Advice appreciated!!