We are trying to build a computer for the first time. When we turn everything on, monitor says: no signal

The parts for the computer:
AMD FD6300WMHKBOX FX-6300 6-Core Processor Black Edition BitFenix Computer Case BFC-COM-100-KKXS1-RP
Crucial Ballistix Sport 8GB Kit (4GBx2) DDR3 1600 (PC3-12800) 240-Pin UDIMM Memory BLS2KIT4G3D1609DS1S00/BLS2CP4
EVGA 500 W1 80+, 500W Continuous Power, 3 Year Warranty Power Supply 100- W1-0500-KR
GIGABYTE GA-F2A88XM-D3H FM2+ AMD A88X (Bolton D4) HDMI SATA 6Gb/s USB 3.0 Micro ATX AMD Motherboard
Lite-On 24X SATA Internal DVD+/-RW Drive Optical Drive IHAS124-14
Sapphire Radeon R9 270X 2GB GDDR5 DVI-I/DVI-D/HDMI/DP Dual-X with Boost and OC Version PCI-Express Graphics Card 11217-01-20G
Seagate 1TB Desktop HDD SATA 6Gb/s 64MB Cache 3.5-Inch Internal Drive Retail Kit (ST310005N1A1AS)

keyboard, mouse, monitor - these all work, as we have checked them on a different computer.

Thx in advance for all help & information.