Might be better if you tell us what you HAVE done so far?
And what happens when you power it on?
Your best bet might be to take it all apart and working on an insulated surface install the CPU, Graphics card, RAM - hook up the PSU and try it.
Standard no-post diagnosis checklist;
1. Did you carefully read the motherboard owners manual?
2. Did you plug in the 4/8-pin CPU power connector located near the CPU socket?
3. Did you install the standoffs under the motherboard?
4. Did you verify that the video card is fully seated? (may require more force than a new builder expects.)
5. Did you attach all the required power connector(s) to the video card? (some need two, some need none, many need one.)
6. Have you tried booting with just one stick of RAM installed?
7. Did you verify that all memory modules are fully inserted?
8. Did you verify in the owners manual that you're using the correct RAM slots? Many i7 motherboards require RAM to be installed in the slots starting with the one further away from the CPU which is the opposite of many dual channel motherboards.
9. Did you remove the plastic guard over the CPU socket? (this actually comes up occasionally.)
10. Did you install the CPU correctly? There will be an arrow on the CPU that needs to line up with an arrow on the motherboard CPU socket. Be sure to pay special attention to that section of the manual!
11. Are there any bent pins on the motherboard/CPU?
12. If using an after market CPU cooler, did you get any thermal paste on the motherboard, CPU socket, or CPU pins?
13. Is the CPU fan plugged in? Some motherboards will not boot without detecting that the CPU fan is plugged in to prevent burning up the CPU.
14. If using a stock cooler, was the thermal material on the base of the cooler free of foreign material, and did you remove any protective covering?
15. Are any loose screws laying on the motherboard, or jammed against it?
16. Did you ensure you discharged all static electricity before touching any of your components? Computer components are very sensitive to static electricity.
17. Did you install the system speaker (if provided) so you can check beep-codes in the manual?
18. Did you read the instructions in the manual on how to properly connect the front panel plugs?
19. Did you turn on the power supply switch located on the back of the PSU?
20. Is your CPU supported by the BIOS revision installed on your motherboard? Most motherboards will post a CPU compatibility list on their website.
21. Have you tried resetting the CMOS?
22. If you have integrated video and a video card, try the integrated video port. Resetting the bios, can make it default back to the onboard video.
23. Make certain all cables and components including RAM and expansion cards are tight within their sockets. Here's a thread where that was the cause of the problem.