sodany,
Does the person who is owed the money, have anything in writing? Does this person have their name on the title to the property, or anything in writing to show they have an interests in the property?
Why isn't the loan being paid back? Is the man just ignoring the requests for payment, or is he trying to sell the property & get the money? The best thing is if the man will sign a paper (use a lawyer) stating the amount of the loan and repayment terms. Or if he would give something of equal value in exchange for the money that was lent.
This does not look good, but the best thing is to talk to a lawyer.
good luck,
lady moon