I have a couple of suggestions but as I don't know this drive too well, someone else should back me up/correct me.
First off, that drive is quite old and I was woundering where you "just got it."
I believe your problem is down to the media you are using. I am sorry to inform you but your drive will not write dual-layer, double-layer, or -R single layer disks. It is strictly a +R single layer drive (I believe). As a result, any blank disks besides DVD+R's will result in some kind of light blinking error code. What blank single layer disks are you using?
Below is a list of media Plextor recomends for this drive
4x +R's are not too easy to find these days (most media is 8x or 16x)
What DVD's did you try to read? It is also possible that the DVD laser has burnt out. Check in you Plextor manual to see what it suggests for your read/write errors. There is a self test that can be run but I'm not sure if this drive can perform the self test.