Initially I though it was a mismatch between sata1 and sata2 since ultrastar is sata2 and an7/built in sil3112 sata controller supports only sata1. I tuned down the hard drive to sata1 using 'feature tool' from Hitachi website. Nothing changed.
Then I found old versions of sil3112 bios doesn't support big hard drives(over 500G?). I went to silicon image website, got latest bios (4284.bin, published on Dec 2008). However, I couldn't flash it to EPROM since an7 has sil3112 built in. Tool from silicon image handles only add-on controller on PCI cards.
On ABIT website, I found their latest bios (an7_19.bin) was published in 2005. It doesn't support big hard drive either.
Now the problem boils down to integrating latest sata bios (4284.bin) into latest motherboard bios (an7_19.bin) and flash it to EPROM.
cbrom came to rescue. the following three commands replaces whatever sata bios in an7_19.bin with latest sata bios:
'cbrom6 an7_19.bin /pci release' releases sata bios component you choose from MB bios file.
'cbrom6 an7_19.bin /pci 4284.bin' integrates latest sata bios into MB bios file.
'cbrom6 an7_19.bin /d' double check 4284.bin is there.
flash an7_19.bin into eprom using awdflash.exe provided on abit website.
set jumper and clear CMOS as AN7 manual says.
The world went back to normal again.