Question Author
Hiya Buenchico
I don't think I've ever been more grateful for someone's input. All of your suggestions were good but although I was now able to get into the BIOS I was stuck with the same problem - I couldn't use the k/b to adjust the settings and the mouse was less than useless. Even restarting the comp confronted me with the options of saving bios settings with or without advanced settings and rebooting into Windows, none of which I could choose.
But there was something you said in your reply which triggered something in my mind and I thought Gigabyte wouldn't be so daft as to make a suitcase with the key on the inside so I tried different USB sockets and found one that was still live; I suppose something I should've done before though I did try and gave up after the first couple.
You are one big STAR, no, the whole Galaxy. Thank you so much.