Why won't my eletric locks work

Hello everyone, its just me Warren, ok here is what is happening now / this time. I was about to lock my doors with the key fob and the remote start i have on there operates like normal. the van starts, the alarm works and when you go to lock the doors with the key fob the alarm chirps, flashes the lights etc. But i don't hear any loud sounds coming from the door locks like i normal would hear. But if you sit in the van and hit the button or key fob you hear it trying to lock but it doesn't. Any idea what it could be? the batteries in the key fob is low i tested that a while ago (that could be the answer but i don't see how). And i check both fuses under the dash and both fuses are good. Lastly, i like how you did with the website it looks really good.. :-D