I don't know what is going on.
Neitehr do we. You are not providing any useful information. We do not even know what version of AE much less anything about your comp, render settings, system specs and whatnot.
The other two gents are correct. More info needed. Look at the link Todd provides.
I'd add a screen shot to that list if it's not there already: if you're brand new to AE and trying to use it intuitively, you may have things totally screwed up and no way to communicate it.
And if you're brand new to AE, you really need to look at this stuff.