Particle system not animating

Just wondering if anyone can help me with a strange problem I’ve been having with particle systems.

I have a blender scene which contains in it various objects including two particle emitters.
I have set both so that they start emitting later in the scene (one starts at around frame 600, the other at around 625). I have set various physics properties on each (velocity, acc) but when I animate (ALT + A) from frame 1 through to the end, they do not animate - the particles don’t move. One of the emitters also has the explode modifier with edge split, and I can see the edges start to split at start frame. But then the physics does nothing.
The weird thing is that if I change the start time to frame 1 and animate again they work perfectly.

Any ideas?

Thanks so much in advance!

David.

Sounds like you need to bake them.

Figured it out. The problem was that I didn’t have the bake settings correctly set. They were on the defaults of 1 - 250.
Thanks Atom!