All done, but no improvement. Thanks anyway.
I've just run Norton WinDoctor and it came up with this, but it can't seem to fix it, could this be the problem?
"C

Program Files\Common Files\InstallShield\Professional\RunTime\0700\Intel32\DotNet Installer.exe" cannot access a necessary file, "mscoree.dll."
How can I access this file? Do I need to?