cilp loop

As Rick already said, you seriously need to read the help and learn how AE actually works:

https://helpx.adobe.com/after-effects/using/previewing.html

Mylenium

A much more detailed description of your workflow and your project would help us help you figure out if there is a problem with your system. I suspect that everything is working normally,

You must be new to After Effects. If you are just trying to edit a video the After Effects is not the right program to use. After Effects is not designed to edit video, it is designed to create shots and motion graphics that cannot be created in an NLE like Premiere Pro. The only reason to have more than one shot in a composition is to create a transition between shots that you cannot do in an NLE. Most of my comps are under seven seconds. I'm working on one now that is exactly 10 seconds and it's taking about 15 minutes a frame to render so the computer is going to be cranking for a long time to render that 10-second composite. I set my keyframes for movement, framing, and timing with the comp set to 25% magnification ratio and auto resolution and no effects, then I turned on all of the effects and checked the comp in about 3 places waiting about 5 or 6 minutes for each frame to fully render, then sent the comp to be rendered using a background rendering app called Render Garden because that's the same workflow the major studios use for complex animation and compositing shots. 

The length of a ram preview depends on your system resources, the composition frame size, and the composition frame rate. A typical consumer-grade system will preview about 10 seconds of an HD comp at 29.97 fps before it runs out of resources and the preview loops. A fairly well-loaded professional workstation might get you a 30 second HD or a 15 second 4K full resolution preview. We all work around those limitations. 

Spend some time with the User Guide, or at least spend 15 minutes using the Window/Workspace/Learn menu to figure out the UI and basic workflow. Watch out for YouTube tutorials posted by enthusiasts because a lot of them contain inefficient workflows and poor explanations. Don't expect to figure out After Effects by just poking around in the UI and hoping things work out.

I hope this helps.