Hi,
No rebooting doesn't work, but I have found a fix. Being such a critical problem I was suprised that it wasn't affecting more people. I think most people use Fire Fox as their browser. I tried FF and it works fine. Thus suggesting that actually it is an IE problem.
The one computer that I have that it works fine on is still using ie 6.
Yes, I do have McAfee and I also thought it was due to McAfee but the fact that it works in FF shows it must be an IE issue.
It has been very worrying, as it is impossible to manage your site without being able to expand settings.
Liz