ok cheers, i tested my PSU on my sisters PC and it shut down aswell.. so its def the problem. it was REALLY hot aswell when i tocuhed the back casing of it (was only on for about 15 mins). it was an old hiper 430watt psu.
id really appreciate if someone could spend 2 minutes and tell me which one to go for (i want to get the right one!) my machine isnt high spec by any means, but i do have alot of applications open at once so id need a decent enough psu.