Car's computer system is not functioning

Of course it can be repaired, but on a Cadillac, there can be over four dozen computer modules. You didn't list any symptoms or problems so it's impossible to know which computers might be involved. What you will find is most mechanics at independent repair shops won't work on this model because of the complexity and unreliability of the electrical system. Too often when one problem is solved, a new one pops up a few weeks later, and they get blamed for it. You may need to take the car to the dealer, especially if the repair involves replacing a computer module.

Sometimes we have to resort to just installing a new computer to see if it is the solution. Independent shops have to buy that computer from the dealer, then, if it doesn't solve the problem, they can't return it. They're either stuck with a part they are likely to never use, or they have to sell it to you anyway. Neither choice is what they want to do. At the dealership, if the computer doesn't solve anything, they can put it back in stock.