So.....being the complete idiot I am - I ran Monolingual on my old Power Book G4 - and removed every language apart from English (u.k.).
I'm starting to think that this is the worst mistake I could've made as I think having deleted "English" and "English (u.s.)" it can no longer boot up.
I turn on the Mac - it loads the grey screen with the ticking clock type icon and then the screen turns blue - however after that....nothing happens. It stays blue (sh*t!)....
Why this is ultra bad news, is because one of my best friends & housemates lent me the thing whilst I wait to get my own Macbook Pro in a couple of months.!!!! So I need to fix it so at least it works (preferably also to save the 30Gb's of her music & irreplacable holiday snaps that are on there).