You don't mention what motherboard this is, or whether the HDD is SATA, but I will take a stab at it. If this system was working and now it's not, the SATA controller has most likely been switched to AHCI in the BIOS. AHCI (otherwise known as NCQ) requires drivers at the install of Windows (F6), they can't be added afterwards. Furthermore, I have seen this exact problem when AHCI is enabled in the BIOS after Windows is installed. It looks like it's going to boot, but then a BSOD. If this is the case, no harm done, just go into the BIOS and set it back and reboot.