I'm not well versed with Mac OS X, but you might benefit from some of the things listed
here. Also, if you plan on buying a new computer, do yourself a favor and buy a used one. It's cheaper, sometimes by a lot, even models that are barely a year old. No need for the best stuff. ACDC might be right, though, it might just be burning out (I wouldn't assume that this is the case and go out and buy something without trying to fix it first, though, that's unwise). I have a bit (read: lot) of experience with computers, and I would be willing to help in any way I can, even without any real OS X experience.
Also, if you actually use CCleaner to clean your registry without manual intervention, you are going to end up fu**ed (excuse the French, but they have perfect words for these things). It might look easy, but when it starts to want to fix things that aren't broken, and you don't stop it, you might just end up with a computer that you can't do anything with anymore, because you need to reinstall the entire OS (but only if you run Windows, teehee).
Do not ever, EVER do this.