Yeah sorry, I realised you'd deleted the prefs folder but didn't edit my post in time, I guess
The folder in Application Data's hidden...you'll have to show hidden files & folders before you'll see it.

Those files from magnetmix should download pretty fast. And since you've tried other p2p & had the same problem, it could be something to do with your ISP. Is there a monthly download limit for your plan? If you've exceeded that, your speeds might drop (you'd have to check this out with the ISP).
I can't find anything in Platinum's acceptable use policy to say that they'll zap your bandwidth if they think you're using too much but...doesn't always mean it's not happening.
Did you update the Java? Try & find that hidden folder & delete it, might make a difference.