I had the same problem on my Lumia 720 and it takes about 6 hours!
I thought it's normal but when search the internet I found that it takes about 15 max.
The solution:
1- charge your phone.
2- click on volume keys and lock screen keys and hold for about 15 seconds.
3- do that several times and will work I hope.
If didn't take your Lumia to the nearest care center.