I had the same problem installing v. 10.4a. After about 8 tries I succeeded by:
o booting in Windows 7 safe mode w/ networking
o disabling the Windows firewall on both private and public networks
o running the installer as Administrator
This completed the installation and brought up the license request form in my browser. After completing the form I got the license emailed to me almost immediately.
o copying the license file to the directory where I installed ModelSim.
Once I verified the ModelSim worked (you have to try simulating a project...compiling works w/ or w/o a license. Then I rebooted to normal Windows mode, enabled the Windows Firewall and lo and behold it still works.