Windows 2000 Com Ports!

Problem: Com1 and Com2 are not working on a Windows 2000 machine. Precise error message ?This device is no longer functioning properly and may need to be replaced. Contact the manufacturer of this device for assistance.?. Crucial point Com portsDO work on the very same machine if Dual booted into NT4.0. Additional factor: machine has a Fritz ISDN card.

Tried SP1 (for W2K), Tried reboot, Tried resource settings = automatic and = manual, machine is a Dan machine and they do use non standard IRQ and IO values. What I am looking for is help from someone who has solved COM port problems on Windows 2000.