accelerator stopped responding now truck wont even start

Hi All,
I have a 2003 toyota v8.

Yesterday I started it up and it was idling very erratically. I could drive it along but the accelerator was not responding, it was just chugging along on the erratic idle.
It then stopped completely and wont re-start-. It doesn't try and turn over at all.

My mechanic cannot get any codes as the machine shows communication error, he also believes this is backed up by the fact that when you turn the key , the dash lights up but the check engine doesn't light up.

Any suggestions greatly appreciated-so far he has looked at it and says fuses, battery are ok and he reckons it will be the computer at a 1000$ replacement. The vehicle has 340,000 km so i am not sure i want to go spending that much when i am not convinced that will remedy it

thanks for any help

Warren