On switch button turns green and immediatley turns

Can you hear the fan spinning on the inside of the PS2? If the PS2 comes on, loads the disc, then shuts itself off, chances are it is overheating and shuts off to prevent damage. There is a small fan on the inside of the Slim PS2 that keeps it cool.

If you press the reset switch and it goes from red to green and immediately back to red without ever turning on, your motherboard is shot. ESD damage.