It is the BIOS version problem, your MB needs the newer BIOS to support the 7th gen CPU.
You will need the 6th gen CPU to update the BIOS first, then you can use the 7th gen i7 7700K. If you don't have the 6th gen cpu, you may go to local PC shop ask for help, or ask your friend for help.
Also you are better to buy other good brand PSU, I think the 480W PSU is not good enough for your PC. It may cause the problem too.