Credit Crisis

Why suddenly we have credit crisis. What happend to those strong parameters considered for stability of banking. Why there is a liquidity problem everywhere and every central bank is pumping money to come out of the crisis. An economic condition where investment capital is difficult to obtain? Banks and other investors become worried about lending funds to corporations and this lead to increase in price of of debt products for borrowers . Sometimes credit crisis is usually considered to be extension of recessions. A credit crisis is usually makes companies impossible to borrow because of lenders are scared of defaults which results in higher rates.