Resolved the problem here is what happened.
Last night my Mouse failed. I replaced the batteries but still it didn't work so I opened up a spare one, a Sandstrom which had a small USB gadget with it. It didn't work so I removed the one at the back of the tower replacing it with the one that came with the Sandstrom which then worked perfectly. The only problem was that then the Keyboard wouldn't work. I changed the batteries but it still wouldn't work and then I had a brainwave, I stuck the small USB gadget taken out from the back of the tower last night and stuck it in a USB socket on the front of the tower.
I know that I have exposed my complete technical ignorance and I will now do it again by asking, why do the experts who build computers create them with the need for two USB gadgets?