I have this problem. I have installed on my performa 6116 the sonnet nubus g3 at 500 mhz. I connect the pds video card on the sonnet nubus slots, then i connect the monitor and everything work fine. But only when the cover of the computer is not closed. When i put on the cover the computer doesn't turn on. what can i do? Sounds like either the Sonnet card or the video card is hitting the top of the enclosure