It just turns and turns, but does not engage, possible PCM issue

1. Due to Covid-19, the car sat for weeks without starting, but use to fine.
2. After that the car just turned and turned but won't engage.
3. Replaced crankshaft position sensor to no avail after mechanic said it was the problem.
4. Then was by told by mechanic it needed a new computer. Replaced that. Worked for 2 weeks. Same problem all over again. Wipers are not working now either. Nothing for lighting in the rear of the car works anymore too.
5. Under-hood fuse box relay was jiggled around, engine engaged. Now the mechanic said the 2000 Lincoln town car fuse relay junction box needs full replacement for computer to work properly-Lincoln doesn't sell that part anymore!
6. If I can find a used 2000 Lincoln town car fuse relay junction box with at least seven inches of wire on each side if it, can I just switch it out and put all new relays and fuses in it myself? I have spent over $1500.00 so far.
7. Going broke, desperate for help. Could this be a possible ground or corrosion issue with the relays, fuses and/or the box itself?
8. Besides lighting this car on fire and just getting a new one, lol, what would you do in this situation, and have you seen this issue before? Everything related to this vehicle not engaging has been replaced except for the above captioned under hood relay junction box.

Thank you in advance for any insight you can provide me with.
Warm regards,

Roger C. In New Hampshire