I have no dept. but bad credit, and my debt to income ratio is really great. How to get a loan?

I average $140K a year net, and I have no current dept. besides 1 car payment and rent. Because of my poor credit I can't seem to get a loan for a home for my family. I've tried the credit fixing companies and all that did was hurt my credit more. I went from a 627 average to a 543 average in 6 months. I can't understand how this is happening, but it is. I would like to find a loan for $250K with land and home as collateral, + 3 cars which I own. Who can I turn to next? I've been working on getting my credit up for over a year with no luck. Please help.