Chippett

Not sure if this is the right place to put this but if anyone can advise me I would be very grateful. My computer seems to be in overdrive ALL the time even though we are not using it. I have a sneeky suspicion that this isn't right... and have tried to work out what it is doing but to no avail. If I go into task manager it is apparently using 100% CPU if that means anything??? I have also defrag'd it and deleted all browing history and cookies on a regular basis in case it is something to do with those, but it makes no difference. I have McAfee virus software which is apparently up to date so hope it isn't anything too sinister... It makes less noise when I am actually using it for something, for example now... Can anyone help please? Thanks in advance. :)