Hi Vik
I can access the BIOS, but I can't find anything relating to enabling USB. However,something very strange has happened! I tried another boot-scan with Avast and it came up with no virus or infections......I had been doing a big clean-out last night and deleted a lot of old folders that had been lurking in "Application Data" I had already removed all of these programs from my computer so I was very surprised to find these folders. Anyway, I deleted the folders, and I am now wondering if the trojan was in one of these. It is the only thing that could make sense to me. What do you think? I am extremely glad to be rid of the trojan, but of course it does not solve the problem of not being able to use the keyboard after Avast's boot-scan. At least I have got time to work on this problem. Now that I am being given the all clear on the boot-scan, I would assume that an ordinary scan will be enough to keep my PC clean?
Thank you all, very much for your time and patience, it is much appreciated. you have been brilliant!
ps. I don't suppose anyone can tell me what to look for in the BIOS?