WIN98 boot failure – dell bios

I’ve just rebuilt my wife’s old Dell XPS T450, including a new system board. Kept the old hard drive. When I started the system, Win 98 failed to boot and gave this message.
Y2000RTC This software is only for Dell bios.

I renamed the windowsfolder to ‘windold’ and installed a fresh copy of WIN98, but the same boot failure occurred.

What can I do?