LG G5 OLED evo TV keeps restarting or will not stay on

The checks in more detail

Plug the TV directly into a wall outlet and not into a strip, and check the cord. Unplug the TV for a minute to clear its state. Keep the TV ventilated, since OLED panels with heavy HDR use get warm, and a TV pushed against a wall with no gap runs hotter. Software causes include an app that crashes the system: note which app was running at the restart and update or reinstall it, and keep webOS up to date in Settings, General, About This TV, Check for updates, since LG patches restart bugs. A TV that restarts when a particular device is connected may be affected by that device's HDMI signal, so disconnect devices one at a time.

Reset the picture settings, as a custom setting rarely causes restarts, but a bad profile might. A restart loop at the LG logo that does not finish needs a power cycle, then a factory reset from the settings if the menu loads, which erases accounts, so back up logins. The OLED panel has pixel refresh routines that run after the TV has been off for hours; the screen may click or the TV may go dark for a moment, which is normal and not a fault.

If the TV restarts with nothing connected, on a good outlet and updated software, a power board fault is likely and LG support should repair it under warranty, which is usually a year with an extension for the panel in some regions. Keep a short record of the restart: the date, the time, what was playing and whether a device was on. Patterns tell you more than any menu. A restart at a set time suggests a timer; a restart during a particular app suggests that app; a restart when the heating comes on suggests a power spike. Bring this record to the support call, because it shortens the diagnosis and shows you have already ruled out the usual causes.