LC17S possible?

Hello,
I am building two HTPC. The components in both are similar,and the basic difference is the case.
1-Silverstone CW01
2-Silverstone LC17S

When i put up together all the components in the LC17S the computer starts, and after a few seconds (not always the same time) it shuts down. I cant even install the O.S.
The HTPC with the CW01 works great. I have done millions of combinations in order to see which is the "bad component". I have even tried to put all the components of the CW01 into de LC17S case. And in shuts down. Works great in the CW01 and shuts down in the LC17S. I am completely lost. Could it be the case?it seems so but where could the problem be? very very

thanks

Have you made sure that you have all the correct motherboard standoffs installed?

I would check that the power switch doesn't get stuck in when you push it to power up. That is what they call a "momentary switch" and is supposed to spring right back out after you press it. If it gets stuck the PC will do just what you describe.

Does the mobo have power/reset switches on it? If so you can try disconnecting the case's power switch and see if it powers up using just the mobo switch.