According to many of the puranasPuranas, it is clearly mentioned that Lord Vishnu is "sanadhana:", i.e no beginning and no end. From his belly button, lord Brahma was born. He started creating things.
By the way he created four sages (I forgot their names) and asked them to help in his creation work. They refused it and they went to "thapa:". Brahma got angry. His anger was "Rudra" or Shiva. After the end of the millions and millions of "chaturyugas" (Krutha, Thretha, Dwabara, Kali) a day will get over for Brahma. The three worlds will die (Bhoo:, Bhuva:, Suva:). A day for brahma is a "kalpa". After some years for Brahma, Brahma will go back to the belly button of Vishnu after the whole 14 worlds die. Then again after a nap, Lord Vishnu germinates Brahma.