I have an HP pavilion pc that wont turn on

you prolly had the jumpers on the new dvd drive improperly set, you want them set to cable select for most cases.

if, on the top or bottom of the dvd drive, it does not have a diagram of which jumper is the master, slave or cable select (usually labeled, cs), then you will haver to look it up in the manual.

if you were connecting the drive to a ribbon cable that is shared with another drive, both drives on that cable must be set to cable select, or one must be set as master, and the other as slave. if there is another drive (optical or hard drive) on that cable, and it is set to the "master" position, the new drive will have to be set to "slave" OR both drives will have to be set to cable select. if you connected the optical drive (set to cable select) to the same cable as the computers primary hard drive (the drive which boots it) and the hard drive is set to master, then it may not boot, until both are set to cable select, or one is set master, and the other, slave.

the other possibility is that you have exceeded the capacity of your power supply, but that is highly unlikely.