System won't boot when powered on, only LED's light up.

I got all the parts for my new computer in the mail yesterday, and was very excited to put it together. After about 5 hours of working on it, it just wont boot. When I power on the PSU, the power LED on the mobo lights up, and when I hit the case's power button, an orange and a green LED light up near the RAM to denote voltage to the DDR. And that's as far as it goes. I've tried resetting CMOS, and I've tried taking the battery out. Nothing works. If anyone can help me get this running, I would be extremely grateful.

My parts:
-GIGABYTE GA-EX58-UD4P LGA 1366 Intel X58 ATX Intel Motherboard
-EVGA 896-P3-1171-AR GeForce GTX 275 Superclocked Edition 896MB 448-bit DDR3 PCI Express 2.0 x16 HDCP Ready SLI Supported
-OCZ StealthXStream OCZ700SXS 700W ATX12V / EPS12V SLI Ready CrossFire Ready Active PFC Power Supply - Retail
-Intel Core i7 920 Nehalem 2.66GHz LGA 1366 130W Quad-Core Processor Model BX80601920 - Retail
-G.SKILL 6GB (3 x 2GB) 240-Pin DDR3 SDRAM DDR3 1600 (PC3 12800) Triple Channel Kit Desktop Memory Model F3-12800CL9T-6GBNQ - Retail
-Western Digital Caviar Black WD1001FALS 1TB 7200 RPM SATA 3.0Gb/s 3.5" Internal Hard Drives - OEM
-SAMSUNG 22X DVD±R DVD Burner with LightScribe Black SATA Model SH-S223Q - OEM

Yes, and my GPU is not in the case right now, for easier access to the mobo. Also, I've tried swapping around my RAM to check for bad sticks. It made no difference.

Ok. I removed everything but the front panel leads. Still nothing. Thanks for the attempt though, by the way.

The CPU power cable is plugged in? Any chance an 8-pin GPU cable got switched for the 8-pin CPU cable?

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