case short or something, please help

Ok i could use some help with this. When my motherboard is outside the case sitting on the box it came in, i can power it up with everything connected fine. but when i mount it in my case it won't power on. the light comes on, on the mobo but when i press the power button the fan LED blinks and thats it. so i put little pices of electric tape on the back of my mobo where the spacers are so the mobo is not touching the brass spacers then it worked for a week. now it does not work inside my case. but outside my case it works fine. is there something wrong with the brass spacers or mobo? no other metal is touching anything. Please help maybe i have missed something.

Specs.

mobo = Asus P5E
Case = Antec 900
CPU = Q6600