New system will only display with motherboard graphics

I have recently built a new system with the parts below. It functions normally without the graphics card installed and the monitor cable plugged in to the on-board graphics, but if I install the graphics card there is no display from the card or the onboard graphics. The case does not have a speaker so I'm not sure if there are any diagnostic beeps.
PCPartPicker part list / Price breakdown by merchant / Benchmarks

CPU: Intel Core i3-3220 3.3GHz Dual-Core Processor (£81.65 @ Aria PC)
Motherboard: Gigabyte GA-B75M-D3H Micro ATX LGA1155 Motherboard (£55.80 @ Aria PC)
Memory: Corsair Vengeance 8GB (2 x 4GB) DDR3-1600 Memory (£34.50 @ Amazon UK)
Video Card: XFX Radeon HD 7850 1GB Video Card (£125.98 @ Dabs)
Case: Zalman Z11 Plus ATX Mid Tower Case (£49.99 @ Amazon UK)
Power Supply: Corsair Builder 430W 80 PLUS Certified ATX12V Power Supply (£35.32 @ Scan.co.uk)
Total: £383.24
(Prices include shipping, taxes, and discounts when available.)
(Generated by PCPartPicker 2012-12-24 15:44 GMT 0000)