welcome to the forums bbbeaver.
is your Plextor the SATA or IDE version? you say it's a 716A then you say they're both SATA/EIDE. do a search in this plextor section for "Asus A8N" and unfortunately you'll find that there is a known issue running this drive with your motherboard..
here you go, but take a look in the Plextor section as well as there are other threads pertaining to this topic:
give the Forum Rules and "posting tips for newbies" sticky a read as well. remember, the SEARCH function is your friend. good luck.