Hello, I purchased a pre-installed Vista machine and added a second hard drive on its own SATA controller and installed XP on it. I control what I boot into using BIOS. This worked fine for a couple weeks. Now, I can no longer boot into Vista (missing NTLDR). However, the boot priority is set to the device that Vista is installed on, but it still boots into XP. When I switch to boot from the XP device, there is no NTLDR. What I think happened was when I installed XP on the second controller hard disk, it overwrote the boot sector on the first (Vista) hard disk. So, I can no longer boot into Vista. I just double checked through Disk Management and verified that XP is indeed installed on the smaller added hard drive, but it shows that this XP drive is the Boot drive and the main, Vista-loaded larger hard drive is System. Ideas?