I recently built a computer. Here is the hardware I am using.

CPU- Intel Core i5-660 Clarkdale 3.33GHz 4MB L3 Cache LGA 1156 73W Dual-Core Desktop Processor
Power Supply- Rosewill Xtreme Series RX750-D-B 750W Continuous @40°C ,80 PLUS Certified, ATX12V v2.2 & EPS12V v2.91
Hard Disk Drive- Seagate Barracuda 7200.11 ST31500341AS 1.5TB 7200 RPM 32MB Cache SATA 3.0Gb/s 3.5" Internal Hard Drive -Bare Drive
Motherboard- GIGABYTE GA-H57M-USB3 LGA 1156 Intel H57 HDMI USB 3.0 Micro ATX Intel Motherboard
RAM- G.SKILL Ripjaws Series 4GB (2 x 2GB) 240-Pin DDR3 SDRAM DDR3 1600 (PC3 12800) Desktop Memory Model F3-12800CL9D-4GBRL

I finished up following the motherboard instructions to put it together and had everything hooked up according to it. I put on my operating system (Windows Vista Home Premium) and it installed completely. The next day, I let the updates for just Vista install (I was going to install Microsoft Office and Mcafee afterwards). The final update was finished so I shut down the computer, unplugged it and let it discharge. I then connected my old hard drive (there was music and a bunch of files I needed off of it),closed the case, plugged it back in, and pressed the power button. The computer started for about a second or two then shut off. All my chassis fans and CPU fan turn on and it sounds like my hard drive is becoming active. I have been taking the computer apart and testing each thing individually and can't pin point the problem.

Can anyone help?

If you can not see the OS desktop, it seems the memory issue. Remove ram , clean it, clean the ram slot and try again.

I think this problem come from your harddrive electric line.

I suggest you disconnect the extra hard drive and try again. If it boots OK, then it means your power supply isn't powerful enough to supply the extra drive and is already working at it's limit. So buy a more powerful supply in that case. Plenty of reviews and info about power supplies can be found on the web - try www.computershopper.co.uk for instance. Hope that helps.

I agree with waterdragon900 about removing the extra hard drive just to test if everything still go fine but for your power supply Power Supply- Rosewill Xtreme Series RX750-D-B 750W it's more than what you need for the stuff you have in your computer right now.
Personally i think that you just forgot to change the jumper from it's master position to slave or cable select position and the computer didn't know on which hard disk to boot...
Hope this help.

Yes i agree that some problem in you hard disk, you just need to check it again.

This post is marked as solved, but what did you do to solve it?