Extreme slowdowns and freezes guest + host on quad core CPU

[realflow100]

When i select more than ONE core in the guest settings my whole system nearly completely locks up and the guest does not get past the "windows boot logo"
Windows 10 x64 pro host

Windows 7 x64 ultimate guest

Memory isn't an issue because if i allocate just one more core my whole OS and the guest slow to an absurd crawl when the windows 7 boot logo is starting

left it running for 2 hours and it was at a black screen when i got back

So i ended the process and set it to 1 core and voila it worked perfectly

Why can't I use more than 1 core without insane slowdowns?

I tried an ubuntu guest earlier and even setting that to 8 cores didn't bring a slowdown at all! not even a performance dip compared to 1 core or 8!
And i only have 4 real cores! What's the deal here with the windows 7??

I have a celeron j1900 quad core 2.42Ghz processor
4GB of ram and intel HD Graphics
(guest allocated 1024MB ram and 256mb graphics but changing those doesn't affect the slowdowns from using more than 1 core in the settings.

and I have the latest virtualbox 5.x version from the main download page. with extensionpack added. No usb 3.0 or 2.0 enabled.

might of posted in wrong section sorry. this might go in "VirtualBox on Windows Hosts"

[mpack]

Configure your VM to show the problem. Then post a VM log file: with the VM fully shut down, right click it in GUI. Select "Show Log" and save "VBox.log" (ONLY) to a zip file. Attach the zip here.

I assume that you're aware that Windows 10 is not a supported host OS.

[realflow100]

I've discovered the problem
When i allocate more than 1 core for the guest to use and look in task manager on my host machine
then right click the virtualbox.exe process and click "affinity" it shows Only a Single Core allocated/selected!! No wonder it was going so slowly! It was practically dying trying to emulate more than one core on one physical core!

And trying to select all of them simply gives a generic error message "Access denied" So it's a bug of some kind...

Heres the log even though nothing really indicates a problem here.