serious electrical problems please help

car was running sweet then a half hour later i got in it to to start it and it sounds like crap,missing and my coollant light came on,so i try to drive it to a firestone,they hook it up to diagnostics,and get code 34 and 42 wich i have no meaning to me,they say that the computer is bad and so i go and get another one for $20.00 put it in,
thinking this should help,well it diddnt and now im still getting those codes and only getting 3.3 amps and not 5.00 readings,
does anyone know were or what kinda problems this is and any info on this subject,man this sucks! i need my ride to work, counting on this!

a code 34 indicates a mass air flow or map sensor (depending on your engine). A code 42 has to do with your electronic spark timing circuit so you may have a crank sensor starting to go.