I can't play with multiple WADs

I used to be able to play mutiple wads with Skulltag and zdoom but now I can't,I would highlight the wads I wanted to play,put them over zdoom or Skulltag and then it would highlight the icon and the name and if I let go,it would play but not anymore. Now I can only play with one WAD at a time. Does anyone know how to fix this? A few days ago,I had a RAM error and everything was gone. Files,applications,etc. I could only use the internet and my Virus blocker and deleter were also gone so I was vulnerable to viruse. After a few days of looking for other stuff in my computer,almost everything had returned,my Doom files,my music,etc. but a few file were still gone. Did this have something to do with it?

http://zdoom.org/wiki/ZDL