That's totally useless. You have not provided any exact system info, no version info for AE, no details about what's involved with your project like comp settings, footage types, effects etc. and no crash logs.
Well thanks for the very supportive answer. I located the answer for my system. For anyone else having issues with lag/reponse from their system when using After effects. There is some system setting that you can set within AE to ensure it is getting enough ram and that it is utilizing all the cores of your processor.
Utilizing all the cores and all the memory is not what you are after. You have to leave resources for other processes and you have to make sure that your system has enough resources to do things like decode footage in the background and process the effects you are setting up in AE. Some video codecs do not respond well to MP rendering so you may have to turn that off or transcode your footage to something that works.
As Myenium said your question lacked the details necessary to even guess what is going wrong. The best option to troubleshoot your problem is to reset your preferences to the default settings then see if the project works. If it doesn't start exploring things like source footage formats for problems. Then start adjusting your memory and MP settings using the guidelines that Adobe has published for optimizing performance.