1996 Ford F-150 Failed Emissions Test

I have a 1996 F150 with 70000 miles on it. It is great condition but when I went to get my PA state inspection, it failed because it didn't pass the emissions test. I was told that it failed because the sensors wouldn't read the proper the codes. I was also told that the problem lied in the engine computer. I tested the computer plug and it has un-interupted power. So now I feel that my only other option is to buy a new computer. I was wondering if this is the only other option before I drop the money on this. Or if there is an another reason this could be happening or another way to test the emissions?

Thanks for help,
Nick