What Happens When a Country Cannot Pay its Loans?

I am not much of a finance person. So it was news to me that countries can go bankrupt when they cannot pay the installment on their foreign debts. I also learned that countries borrow money from the International Monetary Fun (IMF). I wonder where the IMF gets its funds from? Do all the countries in the world pay it on an annual basis or is the IMF supported mainly by the rich countries?

Anyway, the IMF loaned money to Greece and Ireland because they couldnt service their current debts and Greece went on to default the IMF loan too. So that's a bummer. And now everyone is worried that Ireland might follow suit.

So what happens to a country when it goes bankrupt?