1997 Nissan Maxima no spark wont start

First of all, the transmission has absolutely nothing to do with the ignition system. Also, is this car really worth all the effort and money? (Why replace the computer 3 times?)

Now, is the engine cranking over at all? And exactly what are you doing to determine there's no spark?

When there's a "No Spark" issue, the first place to begin is at the battery. Make sure the cables and terminals are tight and free of corrosion. Then check all ground connections, at the engine and frame.

The next step is to isolate the problem beginning at the spark plug and working your way back. If you've eliminated the plugs and wires, then you check the coil packs, connectors and wiring harness. After that, check the crank/cam sensors, including their connectors and wiring harnesses.

After you've eliminated all of these components, then you're looking at a bad computer. In your case, if you've replaced the computer with a known good computer, then your problem is in the wiring/connectors/grounds.

Finally, you shouldn't keep replacing components until you hit the jack pot. This hardly ever works and always costs you money. Instead, follow a logical diagnostic sequence, and thoroughly test each component before replacing it.