Stiglitz explains how the global economy fell and what caused it. Get this and do some reading if you want to understand it.

Available from Amazon (with a different cover), this book is an in depth examination of the many failings of the financial sector. It explains why the changes that are currently being recommended will not be enough to correct the problem and prevent another such collapse. It seems the potential for such catastrophic drops are endemic to the system itself. Thus, the system is in need of major surgery/