Success!
Hello everyone. I've managed to sort it!

Firstly I had to run this:

www.internetinspiration.co.uk/roguefix.htm#uninstall

I'm not sure why, but I had to run it twice. However, I still couldn't manage to get Malwarebytes' Anti-Malware to work. I switched off my laptop and left it for the night.

This morning I tried again and the program would run but not update. So I ran a scan and then re-started the laptop. This time it permitted an update, after which I scanned again.

I was then able to install and update Spybot and after that everything was back as it should be. I'm just about to leave AVG to scan but thought I'd let everyone know.

I really do appreciate everyone offering advice and am genuinely touched that complete strangers took the time and effort to help out.

Thank you.

By the way, these are the programs I downloaded in case any other non computer literate people get afflicted by this problem:

Roguefix:

www.internetinspiration.co.uk/roguefix.htm


Malwarebytes' Anti-Malware:

www.download.com/Malwarebytes-Anti-Malware/3000-8022_4-10804572.html

Spybot:

www.download.com/Spybot-Search-Destroy/3000-8022_4-10122137.html
(Stop Bloody Antivirus Pro 2009, Sat 15 Nov 2008, 14:43, Reply)