Dawn M, mrsuz and Mike,
Thank you all for the help, was still connected to the Internet, but after reading the posts from mrsruz, who had the same problem and Mike giving me the links I have just been through them and applied the recommended solution. Have my fingers crossed that normal service has been restored.
Did try to google the problem before posting on here but must have worded my query wrongly.
I don't have Avast installed on my computer.
Cheers
HeatherR