So to clarify you did not install XP Pro 64 over XP Home SP2, you installed XP Pro 64 cleanly on the SATA drive instead, then put Halo on it? Sounds more like the original graphics/audio/mobo/optical drivers that you had on XP Home weren't updated to XP Pro 64, or were broken when you did the upgrade (incompatible 32 vs 64-bit). When was the last time you went to Windows Update and updated everything possible?