drive’s detecting

dear sir!
i have a GFXcel board and one ASUS cd drive and one Seagate 20GB hard disk.my problem is that some times cd ROM not detected everything is ok like cable,jumpers etc,i did made cd drive master or slave but cd not detecting in secondry master or primary slave .but when i make a single master drive without HDD cd ROM detect.
sir is it a error of power supply or bios?
plz solve this problem with your experience
THANK YOU