if you got launch virtual box in windows 7 64bit fail, you can choose follow version to solve the problem.

VirtualBox-4.3.12-93733-Win => PASS
VirtualBox-4.3.22-98236-Win => FAIL
VirtualBox-4.3.30-101610-Win => FAIL



If you import appliance *.ova fail.

1. Extract ova file as *.vmhd and *.ovf
2. Enter command line:

C:\Program Files\Oracle\VirtualBox>VBoxManage.exe clonehd C:\temp\Jason0401\TW
IN2008-TMP\TW-WIN2008-TMP-disk1.vmdk C:\temp\Jason0401\TW-WIN2008-TMP\test.vdh
-format vhd
0%...10%...20%...30%...40%...50%...60%...70%...80%...90%...100%
Clone hard disk created in format 'vhd'. UUID: c594ce4f-7bf8-4270-b136-e2cd6d2
5e3

3. New a new machine and select the certain *.vhd to import
4. DONE :)


if you want to extend HD setting

1. VBoxManage modifyhd “C:\Users\Chris\VirtualBox VMs\Windows 7\Windows 7.vdi” --resize 81920


[Reference]
https://forums.virtualbox.org/viewtopic.php?f=6&t=38275

http://www.howtogeek.com/124622/how-to-enlarge-a-virtual-machines-disk-in-virtualbox-or-vmware/