1) time was the essence of contract . Full payment was to be received by April 2009
2) in the event purchaser failed to make payment you should have cancelled agreement and forfeited advance payment received
3) since you have found another buyer send a letter to the original purchaser that since he has failed to perform his obligations under the contract you are cancelling the agreement and forfeiting advance payment
4) you are free to sell your land to another buyer
5) full facts should be disclosed to the new user
6) execute sake deed in favour of new purchaser
7) even if original buyer moves court he won't get any reliefs as he. Kept silence for over 6 years