Graphics card

Win98 environment, S3Trio 3D card installed with correct drivers. Display settings include 16 colors, 256 colors, High color (16-bit) but can only get system to display 16 colors. Can select 256 colors or High Color but cannot get either to “stick”. At reboot, defaults back to 16 colors and message states conflict between hardware and settings. How do I get 256 colors to “stick”.