VirtualBox VMs won't startup?

[yayo]

Hi,

i am trying to start my VMs in VirtualBox, but they wont start, i get the following errors:
"Failed to create the VirtualBoxClient COM object.
The application will now terminate.
Callee RC: REGDB_E_CLASSNOTREG (0x80040154)"

and this:
"Failed to open a session for the virtual machine i-forms-0.0.01.
The virtual machine 'i-forms-0.0.01' has terminated unexpectedly during startup with exit code 1 (0x1). More details may be available in 'C:\Users\yqyo\VirtualBox VMs\i-forms-0.0.01\Logs\VBoxStartup.log'.
Result Code: E_FAIL (0x80004005)
Component: MachineWrap
Interface: IMachine {f30138d4-e5ea-4b3a-8858-a059de4c93fd}"

and it hangs in this stage:
"Creating process for Virtual Machine 'machinename' (GUI/Qt) ... (1/2)"

i attached the log, but i removed the beginning of the file as it was not allowed to upload.

VBoxStartup.log

VBoxStartup.log

(116.88 KiB) Downloaded 19 times

[frank]

No error reason visible. Does it help if you uninstall VirtualBox, reboot the host and then re-install VirtualBox?

[lslqyy214@163.com]

No error reason visible. Does it help if you uninstall VirtualBox, reboot the host and then re-install VirtualBox?

I have the same problem.I am using version 5.00, the disk C changed after small will not be able to start the virtual system, also can not after reinstall, attachment is my log, help to analyse the trouble is what reason, thank you

[yayo]

No error reason visible. Does it help if you uninstall VirtualBox, reboot the host and then re-install VirtualBox?

I tried every trick in the book,
1. Installed newer versions.
2. Installed older versions.
3. Updated Windows. (though seems like that's the first reason why it happens).
4. Installed some VB nightly builds.
5. The only thing left to do is formatting my PC, but that will be a major waste of time, if i format and install VB and the same issue comes back after a while.
6. tried running as Admin, installing like admin...etc
7. Re-Registered the VB Service...etc

how the issue appeared: I am working in OS development stuff so i use VB daily, but once i run it and got shocked that problem happens.

[rivetrenuck]

I am having the exact same issue. I installed Virtualbox for the first time last night on Windows 8.1 and it started up just fine and it seems to have crashed upon reboots this morning and after all the methods described in the above post. It refuses to start up. I do not see a solution just yet. Pleased advise if anyone knows.