Joe, a customer, calls a technician to report a remote computer is demonstrate erratic behavior while he is working on it. The technician verifies the files and directories Joe is working on locally…

The described scenario - files and directories completely inaccessible to all applications combined with severe system slowness - is characteristic of the 'files disappearing' symptom, where data becomes unavailable to the user due to malware encrypting, moving, or locking files. The combination of total file inaccessibility and performance degradation is a hallmark pattern of ransomware or destructive malware actively processing files.

File permission changes would restrict access based on user rights for specific files or directories, but would not cause all files to be universally unopenable across every application or produce extreme system slowness.

An application crash affects only that single application and would not prevent files from being opened across multiple different applications, nor would it explain system-wide performance degradation.

Too many startup items causes slow boot times and reduced available memory after startup, but would not render files unopenable in applications or cause all file access to fail simultaneously.