I would definitely factory your networking gear, you don't know what settings are setup, possibly incorrect, so a fresh start is your best bet, then make sure you setup proper dns, proper dhcp range so your statics are in that range,
I would just factory the network, then just power up your router and modem, setup router to work with your modem, set all the dns, and dhcp range. then power up core switch, you can either dhcp reserve, or static, it, make sure those dns match whats in your router, then power up any other switches, and do the same. power up critical devices, and dhcp reserve or static them your choice, then each piece of wired gear, get them static, or dhcp reserve, make sure any gear that you are dhcp reserving, that they are not set to static in the device itself which could cause problems.