Today when i turned in my PC it started as normal but just before the Welcome screen normally comes it my PC decided to turn itself off. After a while i realised (or thought wrongly) that the PSU fan was not working as normal so thought the PC must be overheading and thats why it was turning itself off. So i went out and bought a new PSU but i am still getting the same problem. Any other suggestions?

Heya, welcome to PCHF,

When you flick the power, look inside the case, is there anything other then the PSU that is not working correctly? (especially check the CPU fan)

(Also, have you recently de-dusted your comp a bit? Sometimes it fixes a lot of things )

Yes the CPU fan is working and i gave it a little clean before