Must I sign the employment contract to accept the contract?

I was given a signed employment contract for a fixed 3 years of employment by my employer and I subsequently resigned from my previous job. After resigning my previous job... my new employer induced me into signing a different contract which included a probation period of 6 months. She has now fired me within the 6 month probation period. I had not signed the first contract when I first received it, but I trusted in it (acted upon it) and resigned my previous job because of it. Must I have signed the first contract to have accepted it?