Render Settings? What type of compression? Anything about your comp would also help. We also don't have any idea what kind of a computer you are using or what version of AE, or if you're new... We know nothing so there's not much we can do to help.
Try searching After Effects Rendering in the help files or google and read up.
As mentionerd already, we need exact settings and system info. this could be totalyl unrealted to AE and merely a hardware acceleration issue in your media player or whatever, after all...