To troubleshoot virtual machines in Virtual Box you will need to collect information. For problem determination, it is often important to collect debugging information which can be analyzed by VirtualBox support.

Every time VirtualBox starts up a VM, a so-called "release log file" is created containing lots of information about the VM configuration and runtime events.

The log file is called VBox.log and resides in the VM log file folder. Typically, this will be a directory like this:

$HOME/VirtualBox VMs/{machinename}/Logs

An example of path could be C:\Users\frank\.VirtualBox

When starting a VM, the configuration file of the last run will be renamed to .1, up to .3. Sometimes when there is a problem, it is useful to have a look at the logs. Also when requesting support for VirtualBox, supplying the corresponding log file is mandatory.

For convenience, for each virtual machine, the VirtualBox main window can show these logs in a window. To access it, select a virtual machine from the list on the left and select "Show logs..." from the "Machine" window.

The release log file (VBox.log) contains a wealth of diagnostic information,

• such as Host OS type and version,
• VirtualBox version and build (32-bit or 64-bit),
• a complete dump of the guest's configuration (CFGM),
• detailed information about the host CPU type and supported features,
• whether hardware virtualization is enabled,
• information about VT-x/AMD-V setup,
• state transitions (creating, running, paused, stopping, etc.),
• guest BIOS messages,
• Guest Additions messages,
• device-specific log entries and,
• at the end of execution, final guest state and condensed statistics.

Copy this files and transfer them for support.

On virtual box.org you can find the page about troubleshooting processes.

Reference: https://www.virtualbox.org/manual/ch12.html#collect-debug-info