Short answer:
- Thomas Hobbes was influenced by the events of the English Civil War. John Locke was influenced by the change of government seen in the Glorious Revolution in England a few decades later.
- By "theories about natural law," I'm thinking you are referring to their differing views on what they called the "state of nature." Hobbes believed human beings in the state of nature (governed by natural leanings rather than an organized government) was chaotic and dangerous and violent. Locke believed the state of nature for humanity was a neutral condition, and that experience could teach us the best ways to live according to reason.
Further detail:
Thomas Hobbes published his political theory in Leviathan in 1651, following the chaos and destruction of the English Civil War. He saw the natural state of human beings as one in which persons were naturally suspicious of one another, in competition with each other, and acted with evil and violence toward one another as a result. Forming a government meant giving up personal liberty, but gaining security against what would otherwise be a situation of every person at war with every other person.
John Locke published his Two Treatises on Civil Government in 1690, following the mostly peaceful transition of government power that was the Glorious Revolution in England. Locke believed people are born as blank slates--with no preexisting knowledge or moral leanings. Experience then guides them to the knowledge and the best form of life, and they choose to form governments to make life and society better.