I don't know much about computers, so go easy. When I put a disc.( video ) in the tower, nothing shows on the screen. When I put a music disc. in , I hear music. It has worked in the past.
Any computer store or computer related e-commerce site will sell optical drives. Just put optical drive or DVD RW in your search engine. The cost should be around $30 to $35. At least that's what we sell them for. Be sure you get one with the right interface - IDE or SATA. If your board supports both (it probably does) then go with SATA.
Depending on if you want a burner or just a regular dvd drive then go here and pick what you want. Just make sure you get the right interface, IDE or SATA.
If no luck then can you hear sound through the videos? If you can then it is probably a codec issue. If you can hear sound but no picture, post the file type. to find the file type run the video and it should say somewhere the name. It will say videoname.avi or videoname.mp4 or something like that. that avi and mp4 is the file type.
If it is showing neither sound nor picture then the drive is most probably faulty and you may need to get a new one