PX-712SA help

burner px-712SA
mother board kv8 pro
all cables have been checked and changed
firmware version 1.05
dma and pio mode tried
aspi layer latest from adaptec
xp sp2
dvd dcrypter , nero etc all doing the same thing
good media 3 types tried

i get buffer underun and 100 cpu load when burning dvd’s of any kind

test write fails in plextools latest version with :-

“write error at 25” Unspecified error code (000000)

Check your RAM http://www.memtest86.com/ can boot up with floppy or cd.
How’s the space on your hard drive?
You have buffer enabled in the prgrams I assume.
Any other programs running in the background that may use the cpu?

lots of hard disk space ,burn proof enabled
ram is fine quality corsair checks out fine with that tester and in sisoft sandra pro