Had this problem with my LRP's Comps in my SC10 also, hit it with some compressed air & lightly tapped it to dislodge sand. It worked fine afterwards. I also put tape over the 4 holes to prevent this from happening again.

Also It should have a slightly noticeable but silent click when you press it.
Check the mode button also.
I ran lrps for 10 years, & it's the only problems I ever had.