Can't change display settings

IBM PC will no longer change to 16bit high color display setting. It is stuck on 256 color and when I try to change it says, control panel unable to change display settings, check display hardware. I removed both the monitor & Cirrus video adapterin device manager, rebooted and Windows 98 found them both and installed software. But it still will not change to 16 bit color from 256. Any help would be appreciated.