virtualbox.org

Hello,
After upgrade my motherboard and processor, VirtualBox no longer recognizes 64-bit / VT-x.

HOST:
VirtualBox 5.0.10 r 104061
Windows 7 Professional 64-bit
16GB RAM

GUEST:
Ubuntu 64-bit
RAM 6144MB
Processors 3

I enabled VT-x in the BIOS and I checked this setting several times.
I reinstalled Virtual Box.

I upgraded the mobo from ASUS B85M-G to ASUS B85M-G R2.0.
I upgraded cpu from i5-4440 to i7-4790K.

FAQ: I have a 64bit host, but can't install 64bit guests.

Thanks for the FAQ. Got it working again!

It was my fault. I had enabled the VT-d setting in BIOS, but now I found another BIOS setting named "Intel Virtualization Technology". I enabled it and all is good.

I also enabled Hyper-Threading. These were "hidden" in the BIOS CPU settings: I had to scroll down to see them.