I'm not sure of the MB LED indication, you could go to
Giga-byte and check out the user manuals for the specific MB, or their technical support.
As far as troubleshooting, start with the basics.
Did any/all fans CPU/CASE fans startup when it was turned on?
Double check everything. Reset everything carefully. Check all jumper settings and switch/LED connections.
Pull everything except the bare minimum, which would be CPU/Memory/P/S video/kybd/mouse then try to turn on. It should at least post.
If still no go, try different stick of memory, and/or different memory slots.
If still no go, I would pull the MB out, place on a static bag or other non-conductive surface, and install the mimimum components and test on the bench. If you have different CPU/Memory/P/S, try replacing each in turn, starting with Memory, then CPU, then P/S.
If it works on the bench but not in the case, there is something touching the MB in the case that is causing a short. Try using pastic washers to isolate the MB from the case.