I just downloaded the latest version of AE CC and discovered it won't playback previews. When the play button is pressed, it seems to load into ram but when it comes time to playback, nada. I loaded a project that was created before the upgrade and the comps preview fine but when I create a new comp in the project it won't play. If I bring that comp into a previously created comp (before the upgrade) it will play within the old comp.
Nobody can tell you anything without proper system info or other technical details, including exact comp settings, cache settings, footage used. Start by checking your settings for fast previews and the comp renderer and all that stuff. Quite likely you have some messy defaults there.
My system is a Dell Precision 7800 with dual 3.1 ghz processors, 64 gb of ram, 2 Quadro R5200 8gb video cards, running Windows 10 Pro 64 bit., 3 ssd, 1 2tb (7200 rpm) hard drives.
Comp settings: 1920x1080, 29.97 drop frame fps, half resolution
Cache: 100 gb
Footage: vector shapes and illustrator files
That's odd. I have a fairly similar setup and I'm not experiencing the same issues. Try rebooting, creating a new comp, and trying again with just a solid or shape layer.