I installed SQL Developer 4.01 32/64 bit on Windows 7 32 bit, and JDK 1.7.0_45. The first startup hangs at about 10% of the progress bar.
I renamed the sqldeveloper folder containing user information and the problem continued.
I have McAfee antivirus running and cannot disable it (corporate computer); however in the Task Manager neither McAfee nor anything else is using CPU.
After several attempts, one that lasted an hour, I reverted to the latest version 3.
Follow these steps so we can see where it's hanging.
I reinstalled jdk 7 and SQL Developer 4.0.1 in order to follow the steps you described. Everything started working. I don't know why, but life goes on!
Thanks and best regards,