'''LED #1 should always be on -''' unless the wall cord is unplugged, or, the PS is shot.
That it runs for two minutes seems to point to an overheating problem. '''On a box that old your thermal paste could be shot and need replacement…''' that's a major project.
I would clean out the inside of the machine… leave the back open and set up a small fan and see if it operates any longer… if it does after leaving it overnight you should run AHT and see if it identifies an overheat (or other problem).
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