First, make sure you have updated AE 10 to the latest version, which is at least 10.0.2. Look in Help>Update with AE open.
Next, read these memory and processor recommendations:
http://blogs.adobe.com/toddkopriva/2010/10/please-try-recommended-memory-se...
Dave LaRonde
Sr. Promotion Producer
KCRG-TV (ABC) Cedar Rapids, IA