When I change SATA from IDE to AHCI I can't boot iATKOS s3 from dvd/cd, my dvd/cd rom is first boot device. But when I change it back to IDE I can boot. If I try to install it with IDE i always get "still waiting for root device". Help me.

Motherboard Name Gigabyte GA-790XTA-UD4
BIOS Version GA-790XTA-UD4 F4a
CPUID CPU Name AMD Phenom(tm) II X4 955 Processor
Video Adapter ATI Radeon HD 5850 1GB GDDR5
Ram DDR3 corshair 1666mhz 4GB
HDD Model ID ST3500418AS (500GB)