Dvd's no longer play

a few months ago a roomy downloaded a virus on my computer. I had to hire a guy to come and clean the virus. he did this by first backing up everything on my computer onto discs, then when he was finished he was loading everything back. problem is, his laptop battery went dead before all of the programs were re-loaded.
OK, so I know NOTHING about computer hardware.....but I am having a hard time figuring out why I can view any kind of media from the internet as well as listening to and even ripping CD's.......but when I put in a DVD (which I used to watch on my computer ALWAYS) it says I don't have a driver??????
Question......how can I get this driver? The tech was supposed to come back and put the rest of the stuff back on my computer, but now I can't find his # anywhere. HELP I'm not even really sure what it is I should be looking for. I have an updated Real player and also a Windows Media player. I USED to have PowerDVD....maybe this is what's missing???
<<<<<<lost>>>>>>>