Dear Roopinder,
It is right that the limitation for executing and proceeding for litigation before Court of Law is 3 years. After lapse of the limitation period of 3 years, the agreement to sell becomes regundant.
As you said the agreement to sell is in regard to sale of property/house in respect of which the buyer has flauted the terms of contract and not made payment. That, as stated, the date of execution of sale-deed was set for 17th July, 2012, (which has gone/lapsed).
You havent specified the date of execution of agreement. Barring the date on which the sale-deed is/was to be executed, the limitation for initiation of proceedings before Court of Law is 3 years. You need to issue legal notice calling upon the person i.e. the buyer that the sale-deed was to be executed on 17/07/2012 and that he has not paid the amount of consideration and performed the terms of contract and got the sale-deed executed and registered in his favour on set date. Through the notice you can set a date in specific whereby you call upon the buyer to remain present in the Office of Sub-Registrar of Assurances and get the sale-deed executed and registered in his favour and pay the remaining balance amount of consideration.
In the event, despite issuance of notice (which is a must/mandatory), if the buyer does not turn up and further if you wish to sell the property, you can file suit for declaration, permanent injunction and specific performance of contract, seeking relief from the court to refrain the buyer from creating third party interest over the property by further entering into agreement with 3rd persons on the basis of his agreement and seeking relief directing the buyer to pay the balance consideration and get the sale-deed executed in his favour.
If you are not interested in selling the property, then you can issue legal notice terminating the agreement and inform the buyer that the amount paid as earnest money is forfieted.
Hope this clarifies your query. Feel free to communicate for further assistance.