I didn't realise but I only remembered to update to the newest version of WM on the laptop. I have juts downloaded the new version for the PC and I guess I shall wait and see if the problem persists.
Thanks for your troubles.
EDIT: Installed new Windows Messenger on PC and followed Cookie's instructions again but still the problem persists.
A couple of things regarding his instructions though:
When it says 'close windows messenger' does this mean as in close the window or actually exit the application via rightclicking in the task bar?
My Norton Internet Security does not have the option that is specified in his instruction to uncheck scanning of files or whatever it says.
Thanks for all your help anyway, I guess it's not a huge problem, just frustrating