If your PC is physically restarting, the culprit is almost always (PSU too weak or daisy-chained PCIe cables) or unstable RAM overclocks (turn off XMP).
return
Fortnite uses EAC to prevent cheating, but if this service fails to launch correctly, it will put the game in an infinite startup loop. Fortnite Looping Pc-
Launcher is stuck on an infinite update loop. : r/FortNiteBR If your PC is physically restarting, the culprit
(downloading the same files over and over)—it usually points to a conflict between Fortnite's intensive system demands and your hardware or software configuration. Common "Loop" Scenarios & Fixes PC Reboots or Loops During Gameplay: Overheating: If your PC is physically restarting