>	I tried it.
>	So other PC/AT works fine....
>	I attach the PC-A's dmesg.
>----------
>	PC-A:(Troubled)
>	Celeron300A
>	Tyan S1846S TSUNAMI ATX
>	ENI ENI-155P-MF-C
>
>	PC-B:(Work)
>	P6-200MHz
>	ASUS P/I-XP55T2P4S
>	ENI ENI-155P-MF-C

	what is the IRQ # for the en0 card on PC-B?

PC-A>en0 at pci0 dev 19 function 0
PC-A>en0: interrupting at irq 15

	I suspect that you have 2nd IDE controller on irq 15.  (on some of the
	PCs, even if you disable devices on BIOS screen, devices still occupy
	irq/iomem in random manner)

itojun