While installing laravel through terminal command, my other projects in MAMP htdocs folder got affected and they are not working. I followed this process for installing laravel
Those directions have you symlink the "htdocs" directory to your laravel install, effectively making your htdocs directly useful only for Laravel.
You should avoid this, perhaps by creating a symlink from your laravel build to a directory within htdocs. For example, linking to a directory in htdocs called "mylaravelapp": ln -s /path/to/laravel-master /path/to/htdocs/mylaravelapp.
Lastly, consider using Vagrant or another virtual machine provider instead of MAMP for a server. You'll have to get through a learning curve (potentially), but you'll end up better for it. This creates a virtual server for you, which won't interact with any other parts of your Mac (YOu can make a server per project!).
Here is a guide to get started with Laravel 4 and Vagrant.