Nobody can tell you anything without exact system info or other technical details like what footage is used, cache and MP settings or specific plug-ins.
oh im sorry to bother you, but where can I find all the things you mentioned? I don't exactly know what about them I should mention.
The footage is just a still picture + audio and im just using the presets that came with AE
First, purge memory and disk cash and make sure you have plenty of available drive and cash space. Second make sure that you're still images are not overly large. Second, make sure that you're still images are not overly large. If they are 2-D layers the maximum scale value should be close to 100% at some point in the timeline. If a layer never gets more than 25% it's way too large. If the image is a 3-D layer then the distance between the camera and the layer should be somewhere close to the zoom value of the camera and the scale at 100% or the image is two large. If the problem is not as simple as that then there is something else going on in your composition. We need to know the details.
ahh The thing is, I never had this problem before and I've used AE for about a year, pretty active in animating too (no matter how big the image/close the camera zoom is)
I downloaded the trapcode plug in (installed particular, shine and starglow into my AE), haven't used it yet, but could it possibly be that?
Every now and then I get those issues. Now I am running on a Mac. Rick's advice above about purging the memory is sound. When I have these issues and the purge doesn't work, I shut down AE and start it up again. If it still is not working I would lower the resolution for a lower res preview.