Benedict Take a deep breath, buddy. It's a routine operation, not open-heart surgery. First rule of disk management: Never do anything without a backup. Go grab an external hard drive right now, copy your precious 1.5TB of photos and docs onto it, and unplug it. Once you have a backup, your anxiety should drop to 0.
After that, Windows has a built-in tool called MBR2GPT.exe that does this non-destructively. You don't even need third-party software. Run it from the Advanced Startup command prompt, not inside Windows, to avoid locked file errors. It takes like 5 seconds.
