How does the Statue of Limitation law work for unpaid dept?

I was trying to find out how does the Statue of Limitation work. For example I have an auto loan that has been delinquent since 2003. I got the loan in the state of Nevada. But I remember sending my bills to a Colorado address. What state should I go by? I went through a big hardship which resulted in a repo to my car back in 2003. To this day I am still recovering from that and unfortunately I can't pay them. But the letters still keep coming and the constant credit inquiries. I want to pay what I owe however times are still rough for me and I cannot pay yet. If anyone can help that would be much appreciated. Thanks all!!!