I've got a bunch of empty gems and a soultrap bow. But today it's not working. I don't even get a message that it failed or there's no suitable gem or any message. It was working yesterday.

Re-charge it.

Does it have any Charge left on it?

Go into Inventory, select the weapon and choose Charge (T on the PC). Then select a Soul Gem to recharge the weapon with. The soul gem has to be filled.

Your enchanted weapons don't loose their glow even when the charge has depleted. Only sheathing and unsheating makes it looses its glow. So this can be confusing in telling you if the weapon has any charge left.

Thanks. I completely forgot about that. It holds so many charges I forgot about it. I'd been fighting a lot of bandits and other non-trapable things lately too.