Power/sleep led is blinking green but the screen is not turning on, it's been 3 days like this.

The blinking LED says the laptop is in a sleep mode. Normally a battery disconnect using the button is all that's needed to recover from a hung sleep. You can also try pressing and holding the power button for a while, that also forces a power off, so you can then turn in back on normally. If the issue is a problem with the battery's internal data you need to do a bit more for the full reset. Disconnect everything including the charger. Press and hold the button for 15-30 seconds using something like a bent paper clip. Release the button and wait for 15 minutes or more, that allow all power to bleed off the motherboard. Reconnect the charger, but don't turn it back on until the battery indicator light shows a full battery. Then try to turn it on to see if it fixed it.