Kubuntu VirtualBox

I'm pretty new to Linux and virtualisation so please bare with me.

I have created a Kubuntu virtual machine using Oracle VM VirtualBox. Everything was working fine until today. When the login screen appears and I enter in my password the screen goes to console with some text and then back to the GUI login, the text is only displayed for a split second so I have no idea what the message says. Tried restarting the virtual machine but same error message.

If I were to login via console with the same credentials it logs me in, type in sudo startx (which I read somewhere may bring up GUI), and I then get a blank black screen.

Before this was happening there were some warnings about space running low so i followed this article to increase the partition size which has been completed successfully but issue still remains:
http://jonmifsud.com/blog/increase-virtualbox-disk-size/

Does anyone have any suggestions with how to correct this so I can login successfully without starting from scratch. After trawling through some posts on various Linux forums and trying out their solutions I am still having the same problem. Many of these posts are a couple of years old so hoping since then a solution has been found?

Would be grateful for an tips or help.

Thanks!