The computer takes forever to shut down, then suddenly finishes in two seconds

The long pause followed by a quick power-off usually means Windows is waiting for a service, application, driver, or pending write to finish. Close applications manually, disconnect nonessential USB devices, and test shutdown again. Open Event Viewer and inspect Applications and Services Logs > Microsoft > Windows > Diagnostics-Performance > Operational for shutdown events; note any component and duration named there. Install current Windows updates and obtain chipset, storage, and graphics drivers from the computer manufacturer. Run a clean boot and test several shutdowns. If the delay disappears, re-enable services and startup items in groups until the responsible component returns. Also run DISM /Online /Cleanup-Image /RestoreHealth, followed by sfc /scannow, from an elevated terminal. Do not force power-off during the delay unless the machine is completely unresponsive, because pending writes could be lost. Persistent delays without a useful event should be captured with Windows Performance Recorder for support analysis.