Water won't go through skimmer

[poolcat]

We inherited an old pool but bought a new skimmer and installed it because it was cracked. The water was sucked through from the pool but only at a slow rate (compared to the other skimmer). The new one is furthest from the pump. Yesterday water stopped being pumped through the new skimmer. Is this likely to be a valve problem in the skimmer line or is something blocked in the pipe or is there a leak in the pipe? The skimmer doesn't have any attachment except the pipe that goes straight to the pump. We are complete novices.