The 3 most important things that lenders look at in evaluating you for a loan are income, credit, and assets.
INCOME - you need to prove that you have enough income to afford the payment on any loan we give you, in addition to your monthly payments you are also currently responsible for. Generally the new payment plus your current payments can't exceed 45-50% of your total monthly income
CREDIT - are you responsible with regards to your current debts and do you pay them on time? Also, how much debt do you have? If you show a disregard for making payments on time or all your accounts are maxed out then you could have a tough time getting a loan. If you don;t use credit at all? Then this could be a big issue as well. No credit is almost as tough to work with as bad credit because lenders have no idea if you will be a good risk or not.
ASSETS - There are liquid assets and non-liquid assets. Liquid assets are cash assets or assets that can be converted to cash quickly. Things such as checking and savings accounts, money market funds, stocks. Non-liquid assets take some work to be converted to cash. The perfect example in your case would probably be the equity in your home. It's there, but you can't gain access to it without selling your home or borrowing against it. Assets in relation to getting a loan are usually going to refer to money for a down payment. You'll need to provide a down payment on any home you wish to purchase. A down payment will normally come from liquid assets.
I hope this helps. Like I said, if you can be more specific in why you are being denied for a loan we can be more specific in advising you on what you can do to get approved.
When you say "Why can I get any kind of loan?" If you are already a homeowner you would not qualify for a WHEDA or other First Time Homebuyer programs or grants.
Hope that helps. Wishing you the best in your home and mortgage search.