More than likely one of two things has happened. Either you have lost the SATA raid drivers or you have lost the Partition or MBR on the drive. Asus has raid drivers here that you can redownload and see if installing them fixes the problem.http://support.asus....mp;model=P5NSLI
Looks like the 5th one down is what you need.
If that does not work you may have to try getting into recovery console and thry fixing the MBR.
Boot with the XP installation CD.
When prompted, press R to repair a Windows XP installation.
If repairing a host with multiple operating systems, select the appropriate one (XP) from the menu. If you have only one operating system, enter 1 to select it.
Enter the administrator password if prompted.
To fix the MBR, use the following command:
This assumes that your installation is on the C:\ drive. You will be presented with several scary warning lines the reading of which will make you want to say no. Microsoft is exceptionally vague regarding the conditions under which fixmbr can cause problems although they are clear about the consequences (losing all data on the hard drive), so use this at your own risk.
Type y and ENTER to fix the MBR.
Type exit to leave the recovery console and reboot.
If you do not have a XP CD you can install the recovery console this way.
Download this bootable 7Mb .iso for a bootable Recovery Console:
Burn this iso to a CD and restart the computer with the cd in a drive.