Lease Contract Renewal: New contract never appeared in writing

This is the situation.
I signed a lease contract with my landlord in which states period of time from March 2006 to March 2007 and it is a subject to renewal for additional year (which means till March 2008, but no date is stated in lease). On March 2007, one year lease expired, I entered into "additional year' as a tenant in house, landlord continued to accept the rent. Renewal (new contract for "additional year") never appeared in writing. If I want to move out, am I obligated under the current contract to stay until the lease ends or I become a periodic tenant (month to month based)?
Is that contract still valid or expired?
Otherwise, based on what I am obligated to stay with my current landlord till March 2008?
Need immediate help.
thank you.

If you did not sign it is a month to month unless the lease has a clause that says it automatically renews.