I'm having a similar problem only both my cpu and gpu fans are working fine. When I power it on the monitor seems to be getting no signal and goes to sleep, also the keyboard and mouse get light up. Pretty clueless as to what is going wrong.
Sounds like you also may have missed the 4/8 pin CPU power. It's #2 on the checklist. Check the CPU power, if that doesn't work, go through the other steps.