Yet another update!
Got a £90 motherboard repair done on the old computer (The Machine, as I call it), so it's working again now. The guy in the shop didn't tell me exactly what the repair done was and I've not used that place before so not sure how long it will last. Still leaning towards getting a new computer rather than trying to keep this as my main machine, though, given it's getting on a bit and I don't want to go through this again in a few months when I'm writing up my dissertation. I'm going to mull it over for a day or two then probably order something in the next week or so.
@SdS: That's a fair shout, I suspect I do want the power to be portable - as I'm likely to be moving several times in the next 2-3 years and I'm often having to move my desk across the country (when I visit family for example) I think running a laptop as an all purpose machine probably makes more sense
