I'm having some horrible IRQ issues, and I need help.

I have options in the BIOS for IRQ settings, and there are IRQ settings in Device Manager as well so I'm not sure which settings to change.

The computer is a modified 6792-2HU. I added a video card, wireless card, CD-Burner, DVD-ROM, more RAM, and a 200 GB Hdd.

Pentium 4 (1.79 GHz / Socket 478 mPGA / 400 MHz FSB)
512 MB RAM (PC133)
Nvidia GeForce 4 Ti 4200 (AGP / 128 MB RAM)

The computer worked perfectly with the modifications for well over a YEAR, but yesterday I uninstalled the video drivers and rebooted. I was planning on upgrading to a GeForce 5500 FX card.

I couldn't get it to boot in safe mode or any other mode so I decided to just reinstall Windows since I had a beta version of SP3 installed. I was hoping Windows would reassign everything correctly, but it didn't work. I've spent the day trying to fix it.

I've tried:

- Unplugging hardware I don't absolutely need for Windows to install.
- Only using 1 STICK of RAM.
- Flashed the BIOS with the newest version (made in 1994).
- Set the BIOS to "legacy free" mode to free some IRQs.
- Switching the ACPI IRQ between 9, 10, and 11.
- Installing 3 different versions of Windows XP (SP0, SP2, & 2 version of SP3) multiple times.

I finally got XP with no Service Pack to install.

Right now, it will boot without freezing if I turn it on with my USB mouse unplugged. I'm also having trouble with the new video card. I installed the drivers from Nvidia, but Windows insists that the graphics be 4-bit color.

The new card is a 8x and the AGP slot is 4x. I don't know if that matters, but I hope not. There's also a setting in the BIOS about the video card. It has options for AGP or PCI and 64 MB RAM - 256 MB RAM."Flashing" the BIOS might not have been a good idea here...
Remove the CMOS battery and UNPLUG all power for ten minutes and replace the battery and re-boot.
This will set the BIOS to default settings but it WILL NOT correct an incorrect flash.