Is is IDE or SATA?
If you have an IDE hard drive and DVD on the same cable, check the original hard drive. It should either 'master' or CS (cable select). If it is master, then set the jumper on the DVD to 'slave'. If it is CS, then set the jumper on the DVD to CS. Also, if it is CS, don't swap the connectors between the drives. Sometimes you just have to swap connectors, then you can set HDD to master and DVD to slave.