The fans working don't really mean anything. It sure doesn't take much power to run a fan. A nearly dead PSU will run a fan, but not a system. I'd have to say it's a PSU problem.
You might want to post the complete computer specs. I know you already had another thread about this, but I don't feel like tracking it down right now. You should have just updated that thread so we could easily see what troubleshooting has already been done.