During the boot process, do you see a prompt to enter the RAID setup utility? If so, go into that and make sure the RAID is indeed set up. They do not come set up from the factory, you have to configure them.
You will need a floppy boot disk with the raid controller drivers on it. Look through your package of software that came with it. You should find a cd for the motherboard. If the raid controller is onboard, run this CD in a xp machine, follow instructions to create a floppy disk for the raid controller. If the raid controller is in a slot, then look for a raid controller CD, and do the same thing as above. Then insert the floppy in the server, boot from CD, press F6 when prompted(watch the bottom of the screen) follow instructions.
If you don’t have an internal floppy drive in the server, you’ll have to get an external USB floppy drive.