Can't watch DVD on Samsung SM-352B

I installed this used (e-bay) drive along with another CD-ROM and am able to play games, music, and even picture CD's, but no DVD. I found out that I needed a decoder. Bought one last night from Sonic ($15). Still no DVD. The light on the DVD blinks along with the light for the processor (i guess) and then goes out after a while. When I go to My Computer and choose the drive it says no CD inserted. I know its in there! I have looked (i think) everywhere for a driver thinking this might be the problem. I am a novice with a phillips screwdriver and Windows XP. Please help..............

Hi Mook, welcome to wd forums.

"Used" .. mmmmm... okay so you fitted these drives yourself pressumably, in which case I'd suggest you try unplugging the cd (which I again am pressuming is all ok) & then with just the DVD drive connected try to boot from it using a windoze system disk, that'll at least confirm its got cd function & is wired up ok, then we can get around to looking at your software setup ..