Dvd acting up

hello and what a great site!
my dvd unit (LG -gsa-h22n) was working great month ago or so.now i went to use it the other day and when i put a disk in ,it doesn’t matter if its a cd or dvd. it spins up and then it will reboot my computer. i deleted it and reinstall it again and it still does the same. So this time i have a old Memorex cd player i plugged in start up the computer, tried a cd and it worked! so i thought the dvd unit was no good so i went out and bought a lite-on (lh-20a1h) unit. let it loaded up and put a disk in and it just spins up and down, it does it with dvd or cd disk. i then tried a different IDE cable and still no difference.
where do i start looking to repair this problem?

thanks in advance james