Virtual Box stopped working suddenly

[JRode]

I'm using virtual box on a win8.1 system with 5 linux distributions installed in VB. Every single one of the dists were working perfectly while I was studying for the first part of my CompTIA Linux+ exam, and after passing it yesterday I was going to start studying for the second exam next week and suddenly nothing is working.

I get the error:
VT-x/AMD-V hardware acceleration is not available on your system. Your 64-bit guest will fail to detect a 64-bit CPU and will not be able to boot.

I did my usual troubleshooting procedures, i.e. a google search, and found that this is mostly caused by Hyper V being installed.
I checked if it was turned on, it is not.
I tried to turn it on in order to try to turn it off to see if that would have any effect (hey, you never know), but it actually gave me an error about not being able to install it, the error code led to some sort of conflict with . NET 3.5, I have no idea if this has anything to do with the issue or not.

I also read that some issues could be resolved by clicking on settings, system, acceleration in order to click something there, but the acceleration tab is greyed out now, I looked at the General section of the settings and it only lists 32 bit linux dists now as options.

Does anyone have any idea as to what may have happened?
It may or may not have had something to do with me turning off my computer last night instead of just putting it to sleep as I usually do, i.e. some windows upgrades may have been installed.
I would greatly appreciate any help in this matter.

Thank You,
J

[loukingjr]

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

[JRode]

Thank you for your reply.

1. I did not have any issues installing the 64 bit Linux distributions
2. I did not have any issues running the 64 bit Linux distributions until this morning, i.e. they worked fine from the moment they were installed up until this morning.
3. I already did the troubleshooting steps in that guide, as I wrote in the original post.

I also tried reinstalling VB 4.3.26 and also uninstalling 4.3.26 and installing 4.3.24, neither of these steps worked.

I ended up checking in to what all was installed automatically on my win 8.1 system this morning. The following things were installed this morning:
KB3048778
KB3013816
KB3013769
KB2976978

I took the following steps in troubleshooting possible issues caused by windows update:
1. Uninstalled KB3048778 -> still not working => reboot -> still not working
2. Uninstalled KB3013816 -> still not working => reboot -> still not working
3. Uninstalled KB3013769 -> still not working => reboot -> working

In order to confirm KB3013769 to be the guilty party I took the following steps:
4. Reinstalled KB3013816 -> still working => reboot -> still working
5. Reinstalled KB3048778 -> still working => reboot -> still working
6. Reinstalled KB3013769 -> still working => reboot -> still working

So by uninstalling it I managed to get it to work, yet somehow VB is still working after having reinstalled KB3013769.

It's working, which is great, but I have no idea why:
1. It all of a sudden stopped working.
2. It all of a sudden started working after I took steps 1-3.
3. It does not fail after performing steps 4-6.

I hope that this may serve as a workaround for anyone in a similar situation, and I wouldn't mind if anyone more knowledgeable could shed some light on what exactly happened to my system.

Thank you,
J

[scottgus1]

VT-x can also be "stolen" by another program, or Microsoft itself, before Virtualbox gets to try to take it, leaving 64-bit and multiprocessor guests up the creek. I had this happen once after I installed a trial of BitDefender. Good you got it working!

[JRode]

VT-x can also be "stolen" by another program, or Microsoft itself, before Virtualbox gets to try to take it, leaving 64-bit and multiprocessor guests up the creek. I had this happen once after I installed a trial of BitDefender. Good you got it working!

Thank you for that tidbit of information! Is there any kind of way to force it not to be stolen?

[scottgus1]

Be first in line, so far as I know...