I assume by risers you're actually talking about motherboard standoff's. Should look like this
Make sure you have them oriented correctly. They should screw in until they hit bottom and won't move.
Also, make sure you're screwing them into actual standoff holes, not all holes on the MOBO are.
For ex, in the below pic, the top left and bottom left holes are NOT standoff holes. The ones to their immediete right are.