Error after upgrade:VT-x is not available. (VERR_VMX_NO_VMX)

[Josh@SSS]

I'm getting the Vt-x error as well with VMs that worked fine before (same laptop as the host). Using WIndows 8.1 and VirtualBox v4.3.6r91406. My CPU is an i7 which has hardware visualization built-in and enabled in the BIOS. I haven't touched the BIOS or changed this option, I just confirmed that it was still set.

Settings longmode to off did not work for me and settings VirtEx to "false" did not work, either. I noticed that when I open the settings for my VM I see that the CPU slider is set to 1 and is disabled. I then opened the .vbox file and noticed that the CPU count was set to 2. I set this to 1 and the VM booted fine.

Therefore... this has got to be a bug in VirtualBox! I have hardware visualization enabled yet I can't use more than one CPU.

[Perryg]

Did you select the (64-bit) under the version settings?

[grstatdoc]

I am new to VirtualBox (starting it up to replace XP Mode
Host system: Windows 7 64-bit Professional w/SP 1
Guest system: Windows 7 32-bit Home Premium w/SP1 (virtual disk size=125 GB; 4 GB devoted) ... have the Guest Additions and extension pack added/enabled.
Current log is attached...am not sure how to find the settings to correct this
(I've been trying to get the USB mouse to work properly, e.g., not disable in the host (reverts to the trackpad) and the pointer is "invisible" in the WM screen ... also to have a USB external hard drive recognized properly, but those are separate matters)
I had been working in the machine earlier tonight, but after closing down, I started it once more and got the error message:

Failed to open a session for the virtual machine Stat Crew Machine.

VT-x is disabled in the BIOS. (VERR_VMX_MSR_VMXON_DISABLED).

Result Code: E_FAIL (0x80004005)
Component: Console
Interface: IConsole {8ab7c520-2442-4b66-8d74-4ff1e195d2b6}

I have been reading in the thread on how to resolve this, but admit that I'm not connecting with much of it. Well, guess I'll go to bed and try to wrestle with it later.

[mpack]

The message is self explanatory: VMX (a.k.a. VT-x or AMD-v) is disabled in your PC's BIOS. In order to use VT-x :-

1. It must be available in your CPU (yours does support it, else the error would be VERR_NO_VMX).
2. It must not be disabled in your host BIOS (this is where you fail).
3. No other app can be using it (no Hyper-v, no VMWare etc can be using it when you run VBox).
4. It should be enabled in the VM recipe. For some guests (all 64bit and all Win8, Win2012) this is forced.

You need to check with your PC mfr or your PC manual on how to enable VT-x in your host PC's BIOS. You need to boot up your PC, get into the BIOS (hit F10, Del etc during early boot - the correct key varies), then find the appropriate setting, often called "Virtualization technology" or similar and buried in a security submenu, and enable it. If you see "Virtual directed I/O" - that's something else.

[grstatdoc]

The message is self explanatory: VMX (a.k.a. VT-x or AMD-v) is disabled in your PC's BIOS. In order to use VT-x :-

1. It must be available in your CPU (yours does support it, else the error would be VERR_NO_VMX).
2. It must not be disabled in your host BIOS (this is where you fail).
3. No other app can be using it (no Hyper-v, no VMWare etc can be using it when you run VBox).
4. It should be enabled in the VM recipe. For some guests (all 64bit and all Win8, Win2012) this is forced.

You need to check with your PC mfr or your PC manual on how to enable VT-x in your host PC's BIOS. You need to boot up your PC, get into the BIOS (hit F10, Del etc during early boot - the correct key varies), then find the appropriate setting, often called "Virtualization technology" or similar and buried in a security submenu, and enable it. If you see "Virtual directed I/O" - that's something else.

OK...I had been working OK with the virtual machine until I increased the virtual memory from 3GB to 4GB...then I started to get this error (I went into the BIOS changed the VT setting from disabled to enabled, but still get that error. I think the fact that I had gotten the VM to start OK before, but not now is puzzling.
Guess I'll take another look at the BIOS and post later....

[mpack]

If you want to have an involved discusson then please start your own topic, and provide a VM log file (Minimum information needed for assistance). It's clear that your problem doesn't fit this topic: you don't have the NO_VMX error, and it didn't happen to you after updating VBox.

[amannuc]

I find that one cannot change the file manually. The following worked:
vboxmanage modifyvm <vmname> --hwvirtex off

[kocakbaki]

Hey guys! I ve encountered the same problem, i ve read that i need to enable virtualization technology on my bios but i cant find that setting in the bios.

Does that mean that my computer doesnt support VT? The other question is that I d like to know where you guys put that longmode off code?

BTW my main OS is windows 7.

[mpack]

Nobody here can tell you what hardware features your PC supports or doesn't support, especially when you don't tell us what that PC is. You need to check your PC's user manual or maker for that info.

[telcom]

If you install older version of Vitual box like v3 and 32 bits ubuntu it's gonna be alright.

[mpack]

If you install older version of Vitual box like v3 and 32 bits ubuntu it's gonna be alright.

Ah... the constantly rose tinted good old days.

"Revert to VirtualBox v3.x" is horrifically bad advice.

There is nothing wrong with VT-x support in VirtualBox. What did change is that in v4.3.0 VirtualBox started reporting it as an error if you enabled VT-x on a host that didn't support it. This was easy to do since it was the default on many guest OS templates. Previous behaviour was to silently fall back to software mode. But it's the old behaviour that was wrong, not the new error reporting, because it led to confusion such as people thinking they had installed a 64bit OS when in fact it was 32bit - because without VT-x there's no 64bit support, or multi-CPU support, etc.

Falling back to v3 will also corrupt all your VMs, since V3 doesn't recognize the folder structure used by v4. Some modern guests OSs won't run. And you'll lose useful features of the software such as VM cloning.