ok heres what happened -- My hard drive (Fujitsu MPF3204AH-20g) worked fine before I purhase the new hard drive (MAxtor 40g). First of all, I put my Maxtor hard drive as the master and Fujitsu hard drive as the slave. But my motherboard can not detect both of them. So, I tried to put Maxtor hard drive as master without putting Fujitsu as slave. So, my motherboard can detect my hard drive and It is working OK unitl right now. Then, I put my fujitsu hard drive again as the slave while my Maxtor hard drive still as the Master, but My motherboard still can not detect of them..Why??? Futhermore, I just put my Fujitsu hard drive as the master without putting Maxtor hard drive. In another word, there is just only my Fujitsu hard drive on my pC, but my motherboard still can not detect this hard drive. I has checked the connection/cable and jumper a lot of time eventhough I tried different cable and jumper setting. Unfortunately, it is still not wroking. Also, I tried to connect the Fujitsu hard drive to Promise controller card (add on card), but it is still not working (My Maxtor hard drive can be detected by Promise conntroller card before). So, can somebody help me in this problem becasue I have a lot of important stuff in my Fujitsu hard drive??? Help me,,,,

How new is your motherboard? Also, have you set your BIOS to detect as auto?

Thank for everyone answer my question in the short time. I really appreciate it. I tried to hhok up the hard drive to my friend PC and It still no response. Also, there is no sound coming from the hard drive. So, I guess I should say bye bye to my hard drive.

Patrick. Find out if your hard drive is spinning. To do so, connect it the way it should be but don't fix it on the frame. Support it beside the computer on a pile of books for example. Make sure it won't fall off. When the computer is on, lift the hard drive lightly with one hand. You should feel it turning. If there is no motion at all check the hard drive power source. If the hard drive don't vibrate one bit it's probably dead. Check the warranty on it. Sometimes it just jumpers settings. Check the hard drive web site to find out how to connect it properly. Check jumpers settings for "dual master" or "dual slave" since you want to put 2 IDE hard drives on the same Primary IDE connector. Also if it is a 7200rpm hard drive keep an eye on it. They tend to get real hot. I recommend a fan on it so it stays at a decent temperature. You will extend life on it that's for sure. Good luck.

make sure you update your bios as well, if you connect the hd in question with out connecting the other one and still won't be detected then get yourself another hd

You may check/try all the following things: - First of all is the cable! Try with one HD but once with one connector, once with the other (there are 2 connectors per cable, aren't?). - Some kind of HDD have single and master mode separately. Also, setting "ATA-compliant slave" mode may be necessary. - Get another cable and use the secondary controller.