When you say the graphics card isn't installed, do you mean that you don't have one plugged into the PCIe slot, or do you mean that you don't have drivers installed yet.
If it's the first scenario, the obvious solution would be to install one.
However if you mean you have one plugged in, but you new build isn't POSTing, that's a whole different situation. Basic tips for troubleshooting a non-POSTing computer:
1. Double and triple check that you've plugged everything into the motherboard that needs to be, 20/4 ATX power connector, 12V CPU connector, RAM is fully inserted and installed in the correct slots, video card is fully inserted into the correct slot for a single card configuration and it's PCIe power connectors are plugged into it.
2. Check case connections especially power switch and reset switch.
3. Reset BIOS as per instructions in motherboard manual.
4. Be sure you used the motherboard standoffs, and only used the ones indicated in your motherboard manual.
5. If there was protective plastic protecting pre-applied TIM on your heatsink, be sure that you removed it prior to affixing the HSF.
To get more specific help, you need to post your computer details, motherboard, CPU, RAM, PSU, case, and anything else that might be important.