Well they put it back together and it turned on , with the screen working (further than i got) but apparently it blue screened relatively shorthly after that. They said it was something to do with my computer still thinking it still had the old motherboard back in, saying it was probably an issue with some drivers. Also they said that my hard disk drive may be corrupted, however it didn't show any major issues before this (the occasional blue screen with memory dump, however it did do this maybe 2 times in the last week). They didn't spend much time on it and will look into it again on Monday. Does this seem legit?
I heard there price and it seemed reasonable for the amount of frustration this pc has caused me: £25-£35 (from the initial conversation)