Your PSU is not large enough wattage.....a single R9 280X system is recommended to have a quality 600W PSU according to the link provided below, and that is with NO overclocking of anything.. Looks like you are trying to overclock both your i7 CPU and now the GPU. Probably going to have to get a quality 650-750 watt PSU from Seasonic, XFX, Corsair (except their CX series) or Antec.
http://www.realhardtechx.com/index_archivos/Page362.htm