Computer users who try to run any operating system on VirtualBox may encounter error 0x80004005: "Failed to open a session for the virtual machine." This article will detail how to fix it. Fortunately, there are many ways to do this.

Method 1: Change filenames
This method will help fix the error - "Failed to open a session for the virtual machine" if the previous session was not completed correctly. Fixing this problem is as easy as shelling pears - you just need to rename some files.
- First you need to go to the folder where the files with the VDI extension are located - this is the image of the operating system itself. This directory is often located in the VirtualBox VMs folder at the root of the disk. If you did not find it there, then follow the path C:\Users\owner_name\. VirtualBoxC:\Users\owner_name\VirtualBox VMs\os_name.
- In the directory there will be two files with extensions VBOX and VBOX-PREV. Immediately create a copy of the VBOX file and move it to another folder.
- Now rename the file with VBOX-PREV extension, removing the last prefix. That is, as a result, instead of VBOX-PREV, you should have the VBOX extension.
- Now go to this folder: C:\Users\owner_name\. VirtualBox and do the same, but with the XML-PREV extension.

The error should disappear after that.
Method 2: Update VirtualBox
Maybe the message "Failed to open a session for the Windows 7 virtual machine" appears because your program is outdated or, on the contrary, has been updated to an unstable version. In this case, you need to update it.
- Enter the official VirtualBox website.
- Follow the link releases.
- Choose the software version that suits you.
- Download and install it.
Afterwards the program should function properly.
Method 3: Disable hypervisualization
First, it's worth clarifying that Hyper-V is a virtualization system that is used in 64-bit systems, so this instruction will not help users of 32-bit computers. This system may conflict with the program, which is why the error appears. So, here's what you need to do to solve the problem:
- Open the "Panelcontrols".
- Go to Programs and Features.
- In the window that appears, click on "Turn Windows features on".
- Find the Hyper-V item in the list that appears and uncheck it.
Then it remains only to restart the computer, and after entering the desktop, the application should function without problems.
Conclusion
Three ways were listed above to fix error 0x80004005 in VirtualBox. Of course, these are not all methods, but they should be enough for you, we hope the article was informative for you.