how to reset disks from Raid 0?

hi guys   i have a problem here.   previously i have two HDDs on my M17x and they were set to Raid0 mode. laterly one of the disks was dead but the other one is still OK, so i use that one to reinstall OS. but even after i set the disk mode from Raid0 to ACHI in the BIOS, the installer says it can't not install OS on this disk. i can format the disk, can read/write data on it when plug to an existed OS, can do anything. but unable to install OS on it.   searched somewhere and some people said i need the partner disk of the original Raid volume together to reset the Raid volume and unbind the disks, restoring them to non-raid stats. since the partner disk is gone, how to i do the unbind with only one disk left?   will be appreciated if anyone can help.

Try turning the raid back on in the bios. On my M17x r1 it had another raid option in the bios once you enabled raid. If yours does then go in there and make sure its enabled for the sata ports.

After that boot and hit F10 to enter the raid setup. Move your drive from the right window back into the left window with the delete option. Once that is done reboot and go back into the bios again and turn off the raid for the sata ports. Then set the main raid option back to ACHI.  

If that doesn't do it then something else other then raid could be preventing you from installing windows.

Just to ilustrate morblore's suggestion, here's an article from our support site:

How to Create or Delete a RAID Configuration on the Alienware M17X R1?