Do you have latest bios for your mobo?
6. Enable Intel RAID in BIOS.
The following example is for Asus mobos using AMIBIOS (eg. P4C800-E Deluxe). If your mobo is different, take whatever action is necessary to enable Intel RAID.
6.1. Reattach power, power up the mobo, wait 2 seconds, press DELETE, and enter the BIOS setup.
6.2. Arrow-down to the Main- IDE Configuration screen and hit Enter.
6.3. On the IDE screen which appears, use arrow and +/- keys to set the fields like this:
Onboard IDE Operate Mode= Enhanced
Enhanced Mode Support On= S-ATA
Configure S-ATA as RAID= Yes
Serial ATA BOOTROM= Enabled
IDE Detect Time Out= 35
6.4. Note that when you set "Configure S-ATA RAID= Yes", a new "BOOTROM" field will appear below it; don't forget to set this to "Enabled".
6.5 ESC back to Main, then arrow-right to the Boot screen.