it's a motherboard ABIT SG-72, DDR 256, HDD 40gb Western Digital, CD Rom Recorder, DVD Reproducer. Let me tell you which is the problem: I formated the HDD and installed WinXP Pro SP2. I installed everything... then, when it asked me for re-start... i did it and it couldnt start without the bootable CD. I formated and re installed everything 5 times more... and it never worked. First I supposse it could be a problem of DDR, but no. Then, just for trying, I put a secundary HDD (a slave one) it was formatted but without OS and everything works fine. The bios is well setted 1st.- boot: Floppy 2nd.- boot: CDRom 3rd.- Boot: Hard Disk (and the Western is the first choice) If I remove the slave HDD, the problem return. I tryied the Western Digital in other PC and it Works fine. I really dont know what to do. Can anybody help me? Thank you.