Are you trying to prove one or get out of one? If the former...
Try and prove the elements of a contract, do you have any witnesses to the offer and acceptance.
Can you prove that there was a common intention to create the agreement and any reliance on the contract or any loss that has been suffered because of the contract not being performed.
Was any part of the agreement performed even if not all of it?
Was there any consideration such as money involved, was any money withdrawn for it which can be proven by bank records.
If not money was something done which was part of the agreement eg "I'll provide you with a certain service if you promote me to x, y and z in a certain way". Did one party do something then the other did not fulfil their part.
Do you have any kind of evidence of any part such as witnesses, anything in writing, documents, letters, e.mails or voicemail messages etc...
What is it you want, for the contract to be performed as agreed, to be released from any obligation, to be compensated for loss?