What makes you think that the PS is Good Too?
I've seen customers but everything but a new PS and replace it in what is a new computer that is covered by a Warranty and then they will return it for a Guarantee Claim when all that was wrong is that the PS has taken a Hit from the mains and died.
Just because Fans spin and LED's Light up doesn't mean that the PS is producing the correct Current or even that it is producing the correct Voltages just that there is some power present on at the very most the 12 V DC Circuit. It shows nothing about the lower Voltages Circuits or if they are even working, let alone how much current is present.
Assuming that the 1.5 V circuit is supplying sufficient power to drive the CPU I would be looking at the 5 V Circuit and reading the current output on the 12 V DC Circuits. Yes there should be 2 X 12 V DC Circuits in every modern PS and both need to work.
Of course the easy way is to pull out the PS and fit it to another computer of a similar type and see if it can drive that unit or to just fit a new PS tot he computer and see if that makes any difference.
Relying on spinning Fans and LED's Lighting is no test for anything except maybe that there is Mains Power in the Lead to the computer from the Power Point and even that is a debatable test.
Col