Can't install ethernet or modem

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.

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.