ubuntu 12.04lts virtualbox installation crash

[ubto66]

I had a major crash on my ubuntu 12.04.lts computer system.
I had to push the restart button in order to get the computer to run again.


Info: I installed virtualbox latest edition and the extension pack.
It succeeded, but when I tried to import virtual machines into virtualbox,
from a usb hard drive, the system froze.
I managed to shut down the computer, and later to uninstall virtualbox using synaptic package manager.
And the computer seemed to be ok again.
Now I downloaded virtualbox and extension pack a second time, and tried to install. This time I couldn't install virtualbox. The hard drive began to
squeak, and installation process stuck. I tried to cancel installation but no success. The computer froze, and I had to push the restart button.
Now there is a red warning icon at the top panel (running gnome), and I get this message:
an error occurred please run package manager from the right click menu or apt-get in a terminal to see what is wrong. The error message was “unknown error:<type'exeptions. Systemerror'>'(E:The package virtualbox-4.1 needs to be reinstalled, but I can't find an archive for it.). This usually means that your installed package have unmet dependencies.
End of message.
Now I can't open “update” and
“synaptic package manager” and
“terminal”. About terminal, I can open it but it says The package virtualbox-4.1 needs to be reinstalled, but I can't find an archive for it.
Q: How can I solve the virtualbox problem. I have made backup, so it doesn't matter some data may disappear.
Thank you.