Did you click it 5 times and lock it?
It may be out of charge. Try a different outlet/usb.
Does the button light up without anything attached to the battery (atomizer/
tank/cartomizer/clearomizer/etc)?
If the only way it doesn't light up is when something's attached, the coil's likely shorting out. With many atomizer heads, it only takes the coil to shift the slightest bit for it to touch and short-out on the head assembly surrounding the coil wraps. (it seems like they could have given us more margin of error and space around the coil wraps for many rebuildable atomizer heads which would make for less chance of shorting, more # of coil wraps for more vapor production, and easier to rebuild. But I think it all stems from the standard 510 size which was meant to mimic the size of a cigarette). It can sort of shift on it's own or if you do something like shaking your
tank after re-filling it to soak the wick faster or just by screwing the
tank/cartomizer/clearomizer/etc on.