Left on charger and now Doesnt turn on

You either have

• A bad cable or charger. Can you try these with other devices or alternatively, try to charge another device with your cable
• A defective battery. If your mini still has the original battery, then is is most likely dead or dying. You can take a look at this guide if you want to attempt to replace it yourself.
• A non-functional charge circuit. This would be the case if the two previous suggestions don't solve your problem. This is an advanced repair and requires specialized tools. You would need to find someone who does micro-soldering repairs.