If you haven't done so already, link your debit/credit card with your PayPal account. You will have to use a supported card like the ones that have a Visa/MasterCard logo on. Also you have to make sure that your card is enabled for online transactions. For example if you are using Standard Chartered Bank's Visa Card, make sure it's a "Gold Card" not the "Blue Card".
Once your card is linked, your PayPal account will still have no funds but the balance on your card will be available to PayPal. It can access it whenever the need arises like when you try to buy something using PayPal. It will make the payment using the money in your card.