Bad left I/O board?
My MacBook has had some issues that are pretty weird. On power up, it would have no backlight, no charger led, but the screen itself would come on (you could see it by shining a flashlight on it). The computer would boot, but here's where things get odd.
After about 5 seconds of being on the login screen, the computer would “sleep". The backlight never came on. The computer showed the apple logo and stayed on for the duration of the boot, but soon after the login screen showed up it would turn off. I could wake it up again by pressing a button, and it seems like it's sleeping because if I manage to log in before it shuts off, it wakes up and makes me enter my password again since the computer locked.
I opened the computer up and I found that when I unplugged the ribbon cable that connects the left I/O board to the logic board and booted the backlight comes on and I'm able to use the computer normally except for the fact that it's unbearably slow, the fan is at full speed constantly, and there's no sound. As soon as I plugged the cable back in, however, the backlight dimmed and the computer went to sleep.
The charger light never comes on.
Is this the work of a faulty I/O board or is this a bigger issue like a bad SMC?