Hyundai Elantra problem.

Hi. I know this is a very unusual Topic and that other Forums maybe more suited, but I thought The Comodo family maybe able to help. My wife has a 2000 model 2lt Elantra. The first problem we noticed was that it cuts out under load, when its warmed up. It appears as if a component gives up once heat gets it. Anyway we thought just hook it to Computer diagnostics machine at Hyundai and retrieve the codes, but thier is no communication from the port therefore no data is retrievable which in turn makes it hard to determine what component is faulty. Since then we have also noticed the check engine light(MIL) doesn’t light up with key on engine off as it should so it appears no communication to there either. We have checked all fuses and (MIL) globe and all appears ok. I guess I’m just after some ideas? My guess is ECU problem seeing that no communication with data is possible. Any suggestions or advice will be greatly appreciated. Thanks very much and Kind regards.