Hi Usasma and to EVERYONE else that helped me.
Thanks so much to you all for all your help. Eventually I called in the company that installed everyonr, and very simply, I had fried my motherboard - totally!!
I now have a new one, and new hard drive and now all is working 100%.
Like you Usasma, They told me to STOP fiddling, so have taken yours and their advice!! I will still be logging in to see what's going on, but hopefully I won't be needing any more tech help or advice.
Many thanks everyone !!