The problem might lie with the primary graphics adapter, as far as the BIOS is concerned. Many BIOS'es let you choose whether you want to use an AGP card or PCI card as the primary adapter. Or sometimes onboard graphics as opposed to a PCI/AGP card.
Perhaps this setting in your BIOS is set to the wrong value. I guess XP ignores this BIOS setting, because Plug and Play tells it where the card is. While this theory doesn't explain why your modem has stopped working, it's worth checking.
There would be three ways of getting around it (in order of preference):
- Remove the new graphics card. Put your old graphics card back in, change the relevant BIOS setting, switch off and then put the new card in. (NB - don't boot to Windows while the old card is in...). You could also try resetting to defaults or tinkering with other settings in this way.
- Reset your BIOS settings using the CLR_CMOS (name may vary) jumper on the motherboard. It's usually close to the BIOS and/or battery. Most often between them.
Switch the CLR_CMOS jumper over to the other pins for about 60 seconds to reset your BIOS (With mains disconnected). The battery method that you mentioned should work...did you have the mains disconnected at the time??
- BIOS updates tend to reset the BIOS back to defaults. If you can update your BIOS from Windows, the settings might restore. You should check Compaq's (oops, HP's) website for details. This is a last-resort option!
With regards to identifying the board, does it have an FCCID etched on it anywhere? Model numbers can sometimes be etched on boards in very small print around the edges or between the PCI slots. The exact model number of your PC would help, too.