Hi!
I would start by replacing that fuse on the yellow power supply board (it's the cylindrical thing), as far as I know they need to be transparent and you have to be able to see the small wire inside connecting the 2 ends. They I'd check the capacitors and most other components on the powersupply using a multimeter and replace anything that seems not ok.
If that doesn't do the trick, I'd suggest replacing the motherbord (the green one).