Arghhhh......

This is confusing the hell out of me.

What do I need to buy?

New processor (which? there are a billion and I haven't got a clue what the difference is)
New motherboard (does it matter which one?)
New cooling things - Case cooler? Memory cooler? PSU fan?
What are the noisy things in my PC that need to be quietened?

If anyone could give me a sort of shopping list I would be really grateful.