VirtualBox + Dell laptop VT-x issues

I recently had to use a VM for a uni project, and needed to have access on my laptop & desktop. I haven’t used a VM on my laptop in a while, but didn’t expect to see the following error message from VirtualBox (4.2.16):

VT-x features locked or unavailable in MSR.

I’ve used x64 hosts before with no problems, but I guess my BIOS settings were reverted for some reason (using a Dell laptop with Intel PM45 chipset).

So thinking to myself that this should be an easy fix, I rebooted, enabled VT-x and restarted, but I received the same error message. No amount of changing BIOS/VirtualBox settings, rebooting or otherwise reconfiguring would make this message go away.

I eventually read that it’s sometimes necessary to power down and physically disconnect the machine from power to properly enable VT-x. This solved my problem – I decided to make a note of it here to hopefully help someone else in the same situation.