If you have your engine check light hooked up, then it is really simple.
1. turn engine off
2. short the TE1 and E pins on the diagnostic plug. (use anything that will conduct electricity)
3. turn your key to the on position and count the flashes. If it just flashes regularly then there is no codes.
To reset the computer just pull the fuse on the main power feed to the computer for a few seconds. If you didn't wire it up and don't know what fuse to pull, disconnect the battery. Does the same thing but wipes your stereo and could set off your alarm.