1997 Geo Prizm Battery was connected backwards briefly

Electrical problem
1997 Geo Prizm 150000 miles

My son connected his battery backwards for a few seconds. The car will now not turn on, register the guages, shift out of park or turn the starter. Clearly something has been damaged in the electrical. I have checked all fuses and replaced one. Still does not work. Any ideas on what parts I will now need to replace?
What has been fried?

Thanks