If you want to use Microsoft Hyper-V or Oracle VirtualBox on a Dell OptiPlex 755 system you will need to make/confirm four (4) specific BIOS setttings.
In the BIOS Setup [F2] change or confirm the following settings if you are receiving errors that the computer does not support virtualization.
- Performance -> Virtualization = On
- Performance -> VT for Direct I/O Access = On
- Performance -> Trusted Execution = Off
- Security -> Execute Disable = On