What do you do if you personally mortgage a house and it is registered on title. In the agreement they are to start payments on January 1, 2009 and the buyers have decided they don't want the house now. What do I do if they don't pay?

Foreclose on the home.

What exactly has been signed between buyer and seller? Did they sign a mortgage (promissory) note? Did they give a down payment? Was a transfer of title recorded?