If you are reformatting and installing windows, I would set it it to AHCI and then do your install. Afterward AHCI should work fine. Albeit I have a bit older motherboard that has never worked properly in AHCI, I really am not sure why.
sorry for double post but i got one more question...
Is it dangerous to have it on RAID Autodetect / ATA?? And whats the different.
Also can i reformat my computer with RAID Autodetect / ATA?? If yes, how? because when i insert the cd and restart the computer it will not boot.