cheers for advice guys - it is a faulty RAM chip. I've taken out the second chip and run RAM tester again and its given me the OK. running it again now with the bad chip and will see what happens.
Replacing both sounds like a good idea however the 40p i have to live on at the moment ain't quite gonna stretch! come end of the month i will sort something out. Just wanna get it running for few sets got coming up. Seems to be going fine now

not sure if my mac will take 4gb does anyone know how i can find out?
As for dust - yes this is probably worth while doing so anyway but its not running particular hot (pros bake anyway)
(sorry i should have quoted in this reply - oops

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