If you boot your VirtualBox for the first time and you see something like this:
This is most likely due to VT-x (hardware virtualization) being disabled on your machine. To confirm this is the issue, open the VirtualBox main menu and select the Virtual Machine. Click on the Settings Icon and navigate to the System pane. If the acceleration tab is grayed out like below, then VT-x is indeed the issue.
The process for enabling VT-x will involve entering your BIOS config. The way to do this will vary depending on the manufacturer of your computer. Usually, you can hold down a certain key while booting up your machine (sometimes the F2 key or ESC). However, in Windows 8 and 10, you can use the Advanced startup option to restart your machine in an environment that will allow you to edit BIOS settings. Advanced startup replaced the System Recovery Options menu available in Windows 7 and Windows Vista.
Since you'll need to restart your machine while doing this, you may want to open this article on a mobile device while you go through the process. Below is a video walkthrough of the change on Windows 10:
If you'd prefer to read and follow along with screenshots, here are the instructions for Windows 10.
1. Open Windows settings and select Update & security
2. Select the recovery tab.
3. Find advanced startup and click restart now.
4. Choose Troubleshoot
5. Select Advanced Options
6. Choose UEFI Firmware Settings
7. Click Restart
8. After Machine boots hit the key labeled BIOS Setup/Configuration.
Once you've selected BIOS Setup you should see something like this:
You'll be able to navigate these menus using the right and left arrow keys. Once a page is selected, you can use the up and down arrow keys to select options. The option selected will show up in a different color from the rest.
9. Look for an option like one of the following:
Intel Virtualization Technology
Anything related to Virtual/Virtualization might be the right item
In my case, I found it under System Configuration -> Virtualization Technology
10. Enable the Option you found in step 9.
To enable, you'll need to use the up and down arrow keys to make sure it's highlighted, then you'll hit the return key to open a popup with the available options:
Use the arrow key to change the option to Enabled and hit enter to select it.
11. Save and Exit to start up the computer as usual. You'll see the key in the bottom panel that will do Save and Exit. This is usually the F10 key.
Confirm the exit by hitting the return key again.
Once your machine has booted, open up VirtualBox and check Settings -> System -> Acceleration for your Virtual Machine and you should now see Enable VT-x/AMD-v checked.
At this point, you should be able to boot the machine successfully. If you have trouble getting into the BIOS config via software, you can try the steps in this article to find the key/key combination to use at startup to enter the config.
If you're still having trouble going through this process, you can ask for the help on Ask a Question and (ideally) join a Zoom call from your mobile device.