Autocad lt 2012 will not install from original disc

I just rebuilt my system with a new motherboard and did a clean reinstall of windows 7. I was able to install LT on first try, but resolution was way off, so I unistalled autocad, thinking that maybe I just needed to install it again. Well now it won't install at all I have tried about 4 times with same results. Since I have no real way to get ahold of autodesk, I just don't know what to do? This computer is solely setup for my CAD use, and it is the only one that ever had AutoCAD LT 2012 on it. I did not do the LTU prior to the OS reinstall, and am now pretty much without CAD on CAD system..............What do I do??