SIL Light

Hi Guys,

I have an issue with my MacBook Air, specifically switching it on. Basically, I press the power button, the SIL light flashes once for about 5 seconds, then goes off, then comes back on and I can hear the fans spin up (I have removed the back cover to confirm this). The screen stays black, the keyboard doesn't show any signs of life and the SIL light just sits there. I've tried the usual SMC, PRAM reset, all to no avail. Any ideas?

Thanks,

Mark J