How can I find out which driver/file is being loaded when the system hangs during the Windows 7 boot process?

You can try to enable the No GUI boot option to get rid of the GUI during start-up. OS boot information shows a list of what's loading as it happens - during start-up - so you can know what file is loading if the system is frozen.

In the start search bar type msconfig to open System Configuration. Select Boot tab and tick the No GUI boot and OS boot information

No GUI boot