PC not detecting my dvd-rw

[RuBiQ]

Got a bit of a pc problem and hoping someone might know the answer.

Recently bought a dvd-rw for the pc, so uninstalled the cd-rw and powered down, connected the new sony dvd-rw and booted up, for some reason, it doesnt show unless I manually add new hardware and then it seems to detect it ok, but when I turn the machine off and reboot it, the dvd-rw has gone again and I have to add new hardware again

Anyone know the reason behind this, I have a friend whos cd-rw does the very same thing to him.

Any suggestions welcomed
Thanks

[yosai]

Are the jumpers correct on the back of the device? Master/slave etc.

Is it a SCSI device?

[RuBiQ]

it is set to master as recommended by everyone i spoke too, its just an ide device also..