When you reply to an immediately-preceding post, you will save a lot of forum real-estate if you quote only the relevant portion of its text, or even none of it if you are replying to its overall content.
Use of the CUDA switch has been dealt with
here. As briefly as possible, it is used after you have changed some part of the logic or the peripheral hardware, or reset the MLB. As with all work inside the computer, it is done while mains power is not connected to the Mac, even if you use the mains cable as a ground-return to remove static charge from the Mac and yourself. You can do this only if the mains outlet (wall or power-board) is
switched off, and if the outlet
is definitely grounded.
What are you considering as 'startup'? If the internal speaker was not connected at the time, you could not have heard the chime that follows a successful POST (Power-On Self-Test). Were you using fan noise and HDD spin-up as your cues? The chime is the first of a defined sequence of audible/visible signs that Startup Manager has begun the process, and that 'mileposts' in the startup sequence have been successfully attained: POST, video raster (grey screen), mouse-tracking (pointer movement), Happy Mac, splash screen and desktop. If you are not yet able to see life (raster) in your display, startup is far from being a detectable happening. Further, you can be certain that with no processor installed, nothing else is going to process the startup code in ROM that gets the ball rolling.
Before you hand off resuscitation of the Mac, your own knowledge of what the Mac lacks at the moment will be greater if you have made sure of such basics as battery voltage, RAM DIMM quality, condition and insertion, cable connections, drive condition, peripheral functionality (by replacement with a known-good example, or checking with another Mac), and so forth. If the Mac's configuration has not changed since before the failure, you have both software and hardware to check, and the former can be checked only after the latter has been verified, unless the HDD can be checked in another Mac. Good hunting.
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