Borrow a friend's PC (that has a CD/DVD-rom) and convert your Sonar DVD to an ISO file, using a free utility like ImgBurn.
 
http://www.imgburn.com/
 
Copy the ISO file to your new PC, then unpack it using the same utility as before.  Now you can just install Sonar LE from your hard drive.
 
Or, forget Sonar LE and install the new Cakewalk by Bandlab, now completely free!  CbB is the program that was formerly Cakewalk's flagship program Sonar (but with no limitations like your LE version).