trouble with reinstalling

Hello,
a couple of days ago I installed the base game and a few expansions. Yesterday I upgraded the game to a 1.50 version when it asked me, which I guess I shouldn't have done. The game won't load at all so I came to this place and did a little research about this problem. After that I deleted the base game, event downloaded the torrent again of the base game and torrent of university life as a quite new expansion(because I read here somewhere that this is what I should do). The problem is: I can't start the installation because when I try to mount the discs I can't. It says that those discs have already been mounted so I can't do it again. With those new ones I can't begin the installation, it just won't open. I tried finding those old discs on every place in my computer but no luck... I even reinstalled deamon tools which I used for mounting, but it just happens over and over again... Any ideas what to do?? Please help me! P.S. I deleted only the base game, not expansions.

You probably already have the images needed for install somewhere on your computer. So Daemon Tools already knows them.
What I suggest is either find it in the list of images you have and go from there, or find the old .iso and delete it, then start again.