Ruaidhri - sorry that I can't help. I had a serious problem with the launcher last year and had to eventually copy the install from one computer to another to fix.
I've actually narrowed the problem down to a corrupted .dll file. It's affecting other programs on my laptop as well. From what I can tell the one sure fire way to correct it is to do a reinstall of Windows 7. I'm not even sure I got a disc with the computer. Need to go rummaging through my computer stuff. Not sure what to do if I can't find it, or just plain don't have it.