We develop a structural model of an industry with many entrepreneurial firms in order to investigate the cyclical behaviour of aggregate fixed investment, variable capital investment and output. In particular, we consider an environment in which the entrepreneur cannot borrow unless the debt is secured by collateral and cannot sell fixed capital without liquidating her whole business. We show that, when these entrepreneurs experience persistent idiosyncratic and aggregate shocks, the inter- play between financing constraints and irreversibility of fixed capital is essential to explain several common observations. It helps to explain why inventory investment is very volatile and procyclical, especially during recessions, and why the output and inventories of small firms are more volatile and more cyclical than that of large firms. The model is also consistent with the observations that inventory investment leads the business cycle, and that both fixed and inventory investment are sensitive to the net worth of firms, even when marginal productivity of capital is taken into account.