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It is possible that the battery has failed and you may need to replace it. But first we can reset your iPad and see if it works or not. Press and hold down the Power button and Home button at the same time until it shows the Apple logo or for 20 seconds. When you see the Apple logo, release the buttons and let it boot.
Note : Power button is the button you use to turn off your iPad or its screen. Home button is the round button at front bottom.
Please let me know if that didn't work, so we can continue troubleshooting.
Yes, it could be.
Connect it to your computer with the USB cable and then hold down Home and Power button and does your computer recognize it ?
Connect it to your computer with the USB cable and then hold down Home and Power button of your iPhone and does your computer recognize it ?
Does your computer make any sound ?
Normally connecting to a computer and holding down those buttons will simulate a battery removal reset.
If the phone is not turning on, then it is either the battery or screen has failed. If you had iCloud enabled on it, then all your files should be backed up to iCloud.
Go to www.icloud.com from another device, login to your iCloud account and do you see your stuffs there ?
Call the iPhone and does it ring ? This will tell us if the issue is with the screen or not.
If iCloud backup is enabled, then everything would be backed up to iCloud, like a clone of internal memory. Go to www.icloud.com
Login to iCloud, click Settings and do you see Backup there ? What is the size of backup there ?
I really hope the internal board hasn't failed. If it is not responding to reset, then it must be the battery. You can try replacing the battery. This will not work if this is major hardware issue. You can buy battery and tools from here --> http://bit.do/ccQGy
You can then follow the instructions in here to replace the battery --> https://www.ifixit.com/Guide/iPhone+4S+Battery+Replacement/7111
If the iCloud backup was unable prior to this problem, then there is a chance that your phone was backed up to iCloud automatically (not just a sync, but a full backup). You can check it from www.icloud.com and then click Settings there and it will show backup there. You will not be able to explore backup though there.
You can access and check that iCloud using a computer using this application --> https://www.imobie.com/support/how-to-access-icloud-backup.htm