May I ask why you chose CentOS for a laptop? You mentioned this was your first Linux install, which makes me suspect you might do better with another Linux distribution. CentOS, and Red Hat Enterprise Linux from which it is derived, is usually used on server hardware and virtual machines. It certainly can be installed on a portable machine, but you will struggle more than you would with a distribution that is optimized for installation on diverse desktop/laptop hardware. You're already struggling with boot loader problems; you'll face display and wireless driver problems after that. There are easier ways to get a working Linux installation onto a laptop.