Macbook stuck at boot

Hello everyone,

i ran into a major issue with my MacBook, and am looking for help.

Everything was great. I hung out in OSX, did some work, then rebooted into Windows (Bootcamp) to play a game.

After rebooting back to OSX, i notice that the system is stuck on boot. The apple logo appears, the loading bar too, but it gets stuck at about 35%.

The fans roar up pretty quickly after starting the machine, and they stay running on full until i shut the machine down.

Here is what i tried:

• Rebooted normally a few times - same problem
• Rebooted into Windows (Bootcamp) - success, boots normally
• SMC Reset - no success
• NVRAM / PRRAM reset - no success
• Boot into single-user mode and ran fsck -yf .. works fine but finds no problems.
• Boot into recovery mode - ran disk utility repair permissions and verify disk (some permissions get repaired, but the disk verifies as fine) - also tried resetting ACL - but still OSX won't boot
• Boot into safe mode (using SHIFT-Key) - but even that won't boot
• Activating verbose mode, i found that just before everything gets stuck, there are a few last loglines mentioning VirtualBox. However, since i couldn't even get into safe mode, i cannot even try uninstalling VirtualBox

What i did last time i ran OSX:

Looking for potential reasons why this problem suddenly appeared.

1. This system has been running fine for months. Earlier today i had to uninstall ImageMagick (a command-line tool) using homebrew (with which i had installed it earlier). Afterwards, i installed it along with a specific option, to include a certain module. However, since ImageMagick is not loaded on startup, i don't see how this could be the problem.

2. I moved some files around, had some locked files in the trash, emptied the trash and confirmed to delete also the locked files.

Other than that, nothing out of the ordinary happened.

I did not use VirtualBox for two weeks now. And the last time the computer was rebooted normally, was yesterday, so this is a fairly new problem.

Now i ran out of options. I hope for constructive suggestions.

Please note: Windows 8.1 on Bootcamp (same harddisk, separate partition of course) runs just fine)

Thank you.

I run a Retina MacBook Pro 15" Model, Mid 2015 with the latest version and update of OSX Yosemite