Sadly I have not ever found a true fix. I will still have occasional "everything's frozen except mouse movement" situation on my Dell Inspiron 1720, which is now running Win 10 Pro 32-bit after the end of the insider preview program.
Sometimes a reboot will fix the problem, but sometimes not. It happens far less frequently at boot time but there are quite a few occasions where I boot up into "semi-frozen" mode. The only thing I've found that I believe helps is "not rushing" the machine when it is booting up. I let the disc activity cease once the lock screen is up, then I do the same again once the login to desktop completes. This seems to help in most instances to prevent the issue from occurring right at boot time.
This issue occurs whether I am using the mouse pad on the machine or when I have an external mouse plugged in, which disables the mouse pad (which is a choice I made in the settings). The behavior was no different when I didn't intentionally disable the mouse pad when an external mouse was present.
The only way I can gracefully get out under these circumstances is to hit CTRL+ALT+DEL, tab my way to the power icon, hit ENTER to get the power context menu to appear, use the up arrow key to select either "shut down" or "restart", then hitting ENTER to make that take effect.
This is really, really frustrating because one would not expect an issue with a pointing device, of all things, to trigger this sort of behavior.
If anyone ever finds a true fix I'm begging them to post it (and will certainly do so should I stumble upon same).