Are the fronts of your drawers hitting the cabinet face? Are they hard to operate? They're probably tilted down, because the rear support has collapsed. Here's how I fixed it.
There's a support framework to hold up the back of the drawer slides. It rests on a piece of thin lauan. That in turn is supported on the sides by a 1x1" chunk of pine, which is only held by staples through the lauan panel on either side. The weight of the drawers can pull the staples through, leaving the back of the drawers basically unsupported. The result is the back sags down, the front of the drawers are no longer square to the cabinet face, the drawers are hard to operate, and they make contact with the cabinet face.
This is a picture from after the fix, with the slides properly square to the cabinet face.
I added supports to hold up the 1x1" framing on the sides. It's stapled and glued with E6000, a really sticky SBR glue (like Goop/Shoe Goo, but thinner). On the left side, I added vertical supports against the wall.
On the right, there's not much to glue against, so the supports are wedged in and held in place with the glue. I also glued and clamped the 1x1" against the lauan, since there was no way to get a staple gun back there. There's also a support glued in place against the side wall, which only supports the rear framing. The supports need to allow clearance for the furnace.
