Since you changed everything relevant except the new motherboard, that seems the way to go.
Did you already try to boot and run from a Linux disk? To install Linux? That's free. Installing Windows Vista and Windows 7 as a test is free also, since you don't need a license code to do that.
I have replaced the Motherboard on a Desktop PC and I can't get Windows XP Pro to completely install. - It either freezes or reboots randomly during 'Copying Files' or later stages.
Motherboard: Asus P5NSLI v2.00G BIOS v1801
Processor: Intel Core2Duo 2.4GHz E4600
Memory: 2GB DDR2 667
Graphics Card: ATI Radeon x1650 512MB PCIE
Hard Drive: 160GB Seagate
DVDRW Drive: Optiarc.
Power Supply: 400W
(All PCI cards etc removed, set up as above with Monitor, PS2 mouse and PS2 keyboard only)
Things already tried to solve this issue:
I have substituted with known good devices - Processor, Memory (one stick only also tried) , Hard Drive (single partition), DVDRW Drive, CMOS Battery, IDE Cables, Windows XP Pro SP2 Disk (Genuine Microsoft Copy)
I have removed the battery and reset the BIOS to default values.
Have tried (during Windows install) pressing F5 when prompted for F6 and selected alternatively "Standard PC" and "ACPI Multiprocessor PC". (This was one suggestion I found on the web)
With both drives on IDE Channel 1 as well as on separate IDE channels.
Notes: I sometimes see on the BIOS Screen "IDE Channel 1 no 80 conductor cable installed" (there is) and then either "CMOS checksum error - defaults loaded" OR "Warning! Now system is in Safe Mode. Please resetting CPU or Memory Frequency in the CMOS setup"
Sometimes a restart after a change will yield a completely blank screen and it will require another one to get it to boot.
On BIOS Screen "Installed memory" and "Tested OK" memory values differ.) This is still the case if I substitute with a different memory module)
Any help with this issue would be gratefully received as I am at my wits end!!