plextor drive problem

I just got a plextor px-712a dvd burner the other week, and i have a strange problem. The plextool professional v2.16(and previous version had this problem too) would not reconise my burner. but as soon as i take out my other cd rom(liteon 52x cd-rom) the program would reconise it. I tried different configs, both cable select, and i set them manualy master or slave depending on where they were but had the same problem. Does anyone have any clue on why it would be doing this?

system specs
Asus a7n8x-dx with 1007 bios and newest drivers
athlon xp 2700+
1 gig corsair ram in dual channel
plextor px-712a with 1.03 firmware
ATI radeon 9800 pro AIW

Did you try making the lite-on a slave on IDE0 (with the boot HDD as master), and putting the plextor as master on IDE1 and backup HDD if any as its slave? That worked once for me in a similar situation.