Got some trouble here. When I tried to set the bios to the UEFI mode and then I started my system again, no bootable devices were shown. There was no HD, nor DVD drive. Did something went wrong in the UEFI? In bios mode, everything works Okay. (Hard Disk is not even shown in the post screen.) I think I've figured it out. Not UEFI problem, it's the HD. It needs GPT formatting.