At risk of sounding very stupid I've found a file called 'ModOrganizer.exe.dmp' Is that significant? Thanks for the /profile reminder too.
Well, I don't know what the hell all that was about, but flippin' 'eck, my game is working again! Ok, so MO stopped working but I SO appreciate how easy it was to fix. Thank you Mod Organizer Person! Thank you STEP People!!
And thanks for the responses @rootsrat. I was a bit downcast!