can't run the virtualbox again

[forDream]

OS:Windows 7 x64
VirtualBox Version:VirtualBox 4.3.28 for Windows hosts
I can boot the VirtualBox when my computer is first booting. but I can not restart it if I close the VirtualBox .
I have to restart my computer to open VirtualBox again.
if I do not restart computer, I try to run VirualBox, there is no information.
there are 2 processes in task-manger:VBoxMange.exe & VBoxSVC.exe

the "VBoxSVC.exe" uses all my CPU (25% of the actual use of quad-core CPU)

so...that why ? and what can I do for these ?

[Perryg]

Post the guests log file ( as an attachment )

Also the VBoxSVC.log and VBoxStartup.log ( as an attachment )

[forDream]

Post the guests log file ( as an attachment )

Also the VBoxSVC.log and VBoxStartup.log ( as an attachment )

thanks a lot.
I cannot find "VBoxStartup.log" file.
"VBoxSVC.log" & "VBoxSVC.log.x" in "C:\Users\{MyUserName}\.VirtualBox"