AAA stands for Authentication, Authorization, and Accounting, and it is a framework that provides security services for network access control. Authentication verifies the identity of a user or device that requests access to a network resource. Authorization determines what level of access or privileges are granted to a user or device based on their identity or role. Accounting tracks and records the usage of network resources by users or devices for billing or auditing purposes.
RADIUS (Remote Authentication Dial-In User Service) is a protocol that implements AAA functions by communicating with a central server that stores user credentials and policies.

The symptoms described, such as the operating system taking longer than usual to load and hearing clicking sounds from within the workstation, are indicative of a failing hard drive. Clicking sounds, often referred to as the "click of death," signal the read/write head of the hard drive struggling to function properly. This mechanical failure leads to longer load times as the system struggles to read data from the disk. It is crucial to back up data and consider replacing the hard drive to prevent data loss.