Thank you for getting back to me.
I did go back to the last good configuration at the time but still could only use safe mode. In desperation I tried some other software and found a trojan virus hiding in my registry. The software also found some other junk in the registry which has now been sent into cyberspace! I managed to get in contact with GeekBuddy techs via their website and they gave me a link to a fresh download. Yahoo! All working again thank goodness now back to study!
I have now got my Comodo software cruising along and protecting me. I would like to know how that got past my defences!