No video when playing my DVD-ROM

Hello:
I have audio but no video playing a movie on my pc toshiba dvd-rom. I am using PowerDVD. The error says "Current display mode is not supported.Error code F6F00018.PowerDVD does not support the current display mode. (DDraw Overlay mode is recommended)

Please lower the screen resolution and color depth, for example, 800 x 600 with 256 colors. Or you may adjust the refresh frequency, for example, to 75 Hz.

I have tried lower the resolution but did not help. Also tried 3 other players, but still have problems. I did not change the refresh rate because I don't know how with Windows 98.?

I am presently set at 800x600-256 colors High color(16)bits. ANY SUGGESTION WOULD BE APPRECIATED.

Thanks
Gary