Why won't my Bluetooth keyboard pair with my iPad?

Previously, this was working. All I had to do was simply turn the keyboard on, and when I went into settings to turn Bluetooth on, it paired up easily within 5 seconds. Now, it's not - I keep getting messages that flash up on the screen telling me the pairing was unsuccessful, and that I "should try making sure the keyboard is turned on". Well, it is turned on!! When I press the button it shows the green light that it IS on, but somehow it magically turns off every time I try to pair it, and coincidentally as soon as those annoying "pairing unsuccessful" messages pop up. I'm charging it now, does it have to be fully charged to be able to use it? Why can't I connect the keyboard?