I second the idea that the ramp may be too slippery. I use a fleece liner on mine that I made with uhaul.
I wouldn't put all the food and water on top of the ramp because if they aren't able to get up there that means they aren't eating and pigs really need to graze all day.
To teach mine I normally pick them up and put them halfway up the ramp with my hand behind their butt to help guide them up the ramp. My hand makes sure they can't back down the ramp. Once they get to the top I give them a treat of some sort (like a berry or bit of carrot). Then I put them back in the same spot a few times. Then I start them from the bottom of the ramp, with my hand behind so they can't run away. Same thing, I give them a treat at the top. Typically once i've done all that they will run up the ramp on their own. To teach them to go down I do the same thing, start them halfway first and then from the top. Going down seems to be a lot easier for them to learn than going up, for whatever reason.
It has never taken me more than half an hour to teach mine how to use the ramp. Good luck! Just be patient and entice them with veggies.