Since the problem follows you to other user accounts, that suggests some kind of system-wide problem. Since it persists through Safe Boot, that rules out a problem with some third-party software, such as a font manager program or a driver.
So, let's try narrowing things down a little.
If you try to log in, when the computer shows the desktop and then hangs, can you bring up a Force Quit dialog by hittng Command-Option-Escape? If so, does it list any programs running?
