thanks Ron. I don't think that the motherboard is defective since I got the same old problem between the two motherboards. However, I do think that the "system temperature" is an issue. The system has been on for 15 hours without crashing when I placed a regular fan blowing towards the mobo, unlike before without a regular fan blowing towards the motherboard.. I never knew that higher system temperature may affect how RAID goes. I have a Geforce4 Ti4400 installed (8.5" length AGP slot), so it does raise some heat issues. The case is good in dissipating the heat, but it's not that great in providing good air flow. I think that I might need to drill some holes on my left case panel to place some fans on it.

Brendan:

As far as I know, Tyan Tiger MPX doesn't come with RAID, so this issue may not affect the Tiger. Both Chaintech 7KDD and Asus A7M266-D have an AUX power connection, so there are a standard ATX plug, AUX power plug, and ATX-12V plug. All of them are plugged in. I'm not sure what does AUX lead do exactly. The system will work even without connecting the AUX lead. Nevertheless, when disconnecting the ATX-12V lead from the motherboard, the system doesn't even post at all! Can your system post even without the 12V lead?