Can't install ethernet or modem

[Beverley D]

I am dealing with a P4 computer on an Aopen AX45-V with LAN motherboard.
The problem first came about when attempting to open a dial up connection
"No modem connected". (The installed modem Aopen FM56-PLX had been
working previously.) In device manager the ethernet controller and pci simple communication device both appear with a yellow ? and it says "drivers not installed" Code 28. When I try to install the drivers from the manufacturer's software I cannot. I have tried every method in device manager. It says the wizard cannot find any software on this computer for your device. I have tried the modem in another computer and it installs and works fine. When I go to phone and modem options, modems, there are none. If I try to add the standard 56k modem I get the same results as above. I was told I must have some corrupt files so I reformatted and re-installed Windows XP. Still doesn't work. I am quite sure the modem is ok, the new Windows install went perfectly.
If it were only the modem I would still be suspecting something with the modem itself, but the ethernet adapter is showing up exactly the same way. Would my next step be replacing the motherboard?? I have been tearing out hair for several days and could sure use some advice. Thanks.

[NooNoo]

Welcome to Windrivers BEverley, but please do not post the same problem in two forums. This thread is locked in favour of the one I already answered in Tech to Tech.