The first step in troubleshooting any network connectivity issue is to identify the scope and source of the problem. The technician should check if any infrastructure changes have been made during the user's absence, such as updates, patches, configuration changes, or hardware replacements. These changes could affect the network settings, firewall rules, permissions, or compatibility of the user's device or the server. The technician should also verify if other users or devices can access the server or if the problem is isolated to the user's device. By determining if any infrastructure changes have been made, the technician can narrow down the possible causes and formulate a theory to test.
References
Chapter 5: Hardware and Network Troubleshooting
How to fix HTTP 500 internal server error?
Remote desktop connection: An internal error has occurred