Without knowing anything about your settings, your version of AE, system info and so on nobody can tell you anything.
AE CC 2015
Windows 7 64
-intel i7 quad-core
-12 GB ram (9 of it allocated towards adobe products)
-2GB nvidia GTX 950
as for settings are you refering to the settings I use for Particular or AE in general(both?)?
Link to Particular settings for both particles and emitter:
I'll upload a picture of my other settings depending on which area of preferences you're looking to see. I really don't know much about AE so I'm just getting to know my way around it.
Are you looking through the active camera?
Try setting the blend mode on the solid layer you have the trapcode effect on to normal instead of add..
Select the layer that has particular applied then press the U key twice to reveal all modified properties. In particular start with any modified particle settings and reset them one at a time until you see something. If you can't find it right away reset the whole effect and start again. If you see nothing with the default settings then there something else wrong.