Couldn’t open port – modem error

I get the error message “Couldn’t open port” when I run the modem diagnostics on my ISA PNP US Robotics 56K internal fax modem. I have Com 1 & 2 installed and the modem is on Com 3. The diagnostics ran okay when I first installed it, but upon reboot, I get this error. Actually, I got this error the first time I installed it, then removed the modem (both from system properties & physically) reboot, removed com 1&2, installed the modem, physically, then reboot. Win 98se installed all three and the modem appeared to be working. Upon reboot, I get the Couldn’t open port error. What next?