Older PC games (pre-2010) often use disc-check DRM (SecuROM, SafeDisc, StarForce, Tages) that demands the physical disc even after full install. These DRM drivers don't work on Windows 10/11 (16-bit installer / kernel driver blocked).
Mount ISO → launch game. If "Insert disc" persists, try fixed .exe. If still fails, game may have secondary check (registry, file hash) — search "[Game Name] no cd fix Windows 10".