Answer Description

Event Viewer is a program available in Windows operating systems that shows a log of errors, events and messages from the operating system and applications. This is a great place to start when trying to diagnose an issue. For example, if an application crashes or an unexpected power loss occurs you may find information in Event Viewer that will clue you in on what is happening.

Wikipedia

Event Viewer is a component of Microsoft's Windows NT operating system that lets administrators and users view the event logs on a local or remote machine. Applications and operating-system components can use this centralized log service to report events that have taken place, such as a failure to start a component or to complete an action. In Windows Vista, Microsoft overhauled the event system.Due to the Event Viewer's routine reporting of minor start-up and processing errors (which do not, in fact, harm or damage the computer), the software is frequently used by technical support scammers to trick the victim into thinking that their computer contains critical errors requiring immediate technical support. An example is the "Administrative Events" field under "Custom Views" which can have over a thousand errors or warnings logged over a month's time.