First off, which wires got crossed? coil pack wires, or some other wires, be specific, exactly where they are going to and how did they get "crossed"? Did they spark and short out or just placed on the wrong connections?
EVEN WITHOUT KNOWING ANYTHING MORE, I CAN TELL YOU THAT YOU NEED TO CHECK ALL OF YOUR FUSES! 90% OF ELECTRICAL PROBLEMS ARE DUE TO A BURNED OUT FUSE!
That's where you always start anything to do with electrical problems, fuses are easily changed and cost less than a dollar. A dealership will charge you $100 to check and change a fuse, plus $5 for the part!
Why were the coil packs changed out? What was the car doing that made you change the packs? No spark? Tested for no spark prior to replacing them? Fuel pumps provide fuel, so if there's no gas then it could be a fuse or a bad fuel pump. You'll hear the fuel pump spin up right after you turn your key to the on position. it will make a "werr" sound and stop. That means it's good, it built up pressure in the gas line, so if you hear that then it could be a fuse to another part of your car, look under the hood for fuses and under the dash and even in the kick panels. there are also some relays in the kick panels of some cars, they will go out or stick sometimes. The chances of your computer going out is not likely. I hear people talk about replacing them and can only think that they must have modded them with some aftermarket kit that will do nothing except make your car perform worse than ever. that's the most likely cause for them to brake. They rarely will be a problem if they are left alone.
Wires connected wrong will most certainly blow a fuse before anything can get fried, That's why they are there. I'm willing to bet your problem is fuse related or fuel pump is bad. But if it is a fuse, I wouldn't go back to that mechanic again. I'd also let him know that it was a fuse and see what he says.

One more thing fuel pumps usually will have tell tale signs that they are going bad, when the car has been running for a while the pump gets hot and will stop spinning, once it cools down it will start back up and run till it gets hot again. If you drive with a 1/4 tank of gas or less most of the time, you will shorten the life of the fuel pump greatly. they rely on the cooling of the gas surrounding them to dissipate the heat, without it they will burn up very quickly.

First thing, did you uncross the wires? If not, start there. Second, listen for fuel pump to cycle a prime at key-on. If uou hera pump, then uts not there. Third, assuming the pump is good, check each plug for spark. Could be a bad coil from factory. Was it individual coils or a master pack? If seperate coils and no spark at all, then check fuses and pcm. Recheck all connectors. Hope this helps.

Changing a coil pack will not cause a computer to go bad after words. the fuel pump possibly a coincidence. fuel pressure has to be checked with a gage to check out the pump. if this happened after you changed the coil then recheck your work for something you did not re-connect as this sounds more like your problem and did you get your firing order corrected.

Find a new mechanic who is able to diagnose this problem. Sounds like you are dealing with a parts changer. My guess is the wires still arent routed correctly, and neither the computer or fuel pump are at fault.