The 450w power supply gives me some pause; in theory it is enough - depending on what other things you have in your computer, but I rarely recommend less than 550, especially for game like 14 that pushes all your components to their max. What was the PSU wattage in the old system? If its higher than the 450, I would suspect that as a possible culprit. Usually when you have to hard-switch the computer its because of a power issue or a heating issue (power issue could be a short somewhere, or a lack of power).

In most cases, swapping the hard drive shouldn't matter. The system is supposed to just stop using the old drivers, and start using the new ones. It -is- possible that it got muddled up though, and if the time it takes to reinstall windows and FF14 isn't too much, it certainly wouldn't hurt to try - especially because it could clear up any number of issues that could cause that sort of problem. Up to you if you want to try that or not (I will say, however, that having just reinstalled windows and FF two nights ago, I noticed a HUGE speed increase playing the game; cluttered HD makes for slow game play because how it loads the models).