ECU failures, what causes?

[bwh13]

I'm trying to figure out if my ECU got fried, what would have caused it. Current 413 Red label ECU with AA chip would not start my car, and wouldn't start the test car at a local shop. They are going to replace the chip with a stock one and see if it will start their car.
I'm guessing that if a stock chip starts their car, then the AA chip is not working properly. If the stock chip won't start their car, is the ECU toast or can it be fixed?

What would be the way to determine what caused the ECU to fry?

I have:

S52 w/OBDI conversion parts
525i engine harness that I checked all the wire colors and connectors on to make sure they correspond with the correct component they are attached to.

Treehouse adapter they built for me with the S52 OBDI 525i harness to 88 325i chassis.

The only odd thing about trying to start car (other than it not starting) was the ICV humming when key in 'run' position. Engine cranks just fine. No power to fuel pump or oxygen sensor relays. Main relay has power, ECU has power. Changed fuel pump and oxygen relays. Fuel pump relay (and thus the pump) works if wire from ECU is grounded.

Harness grounded at passenger shock tower. Engine grounds on both sides from pan to frame rail and passenger engine arm to frame rail.

[matt]

Short circuits and water damage are the usual causes.

[static]

try taking it apart and cleaning with special solution for PCBs, i heard this helped some

one reason DMEs get fried are bad coils (the power transistors that drive coils get fried)