A quality 500W PSU would be more than enough; a 380W Antec Earthwatts would run it with no trouble at all, or a 400W Corsair CX.
That Corsair Cinema clip is a Favorite; another Chokemax bites the dust! Too bad they often kill other parts when they die like that. Linkworld is similarly crappy.
Your drive problem is not likely related to power. The 7200.11 Seagate drives were notorious for problems. Back it up and replace it under warranty before it takes your data with it.
Edit: A quality 500W PSU can handle almost any single video card (except the HD5970). Unless you plan to run multiple cards, that's all you need. What is your monitor resolution, and what games do you play, or want to play, on high settings?