I've been running Ubuntu 12.04 LTS on my PC for about 2 months (I had Lubuntu earlier on). It's been doing fine until the last update on Saturday. The first time I switched it on after the update (on Sunday) the screen was all black with only 2 lines in the top left-hand corner - they looked like this:

'Ubuntu 12.04 LTS my username-desktop tty1
my username-desktop login:

When I put my login and password in I got a message:

Welcome to Ubuntu 12.04 LTS (GMU/Linux 3.2.0-45-generic i686)
*Documentation: https://help.ubuntu.com

I've switched it off and on 3 times with the same result. As I didn't have a clue what's happening I re-installed Ubuntu from a CD. The 1st time after re-installation it switched on fine, but the 2nd time - the same problem occurred.

I kept switching in off and on and eventually the normal login screen appeared. It was fine throughout Monday and Tuesday and Wednesday morning - and suddenly, when switching it on on Wednesday evening - the same black screen. So I switched it off and on twice and on the 3rd attempt it was normal.

Can anybody tell me what this means?

I've tried to find info on the Net and found something about X window (or server?) not working properly or problems with Ubuntu desktop. I thought I have the normal Ubuntu desktop installed, but I'm not sure of anything anymore.

I'll be grateful for any help.

I got similar screen on Ubuntu 13.04 when I need to login via tty. (On normal login screen, you press Ctrl-Alt-F1 to enter tty login) When you want to leave it and login normally, you press Ctrl-Alt-F7. Maybe it's a stupid suggestion, but have you tried Ctrl-Alt-F7 to get the normal login screen? I guess it wants to make you login without graphical interface, but if sometimes it works normally, then I don't think it should be an issue with X window manager.
However, maybe the problem is different and I am completely wrong.

Thank you Adalee.

Your suggestion is most definitely not stupid as I didn't know about Ctrl+Alt+F7.

I guess as I'm still so much of a Linux newbie that I don't know about the basics

Thanks for that.

You're welcome
And don't be afraid, I was using Linux for almost a year until I found out something like logging without GUI actually exists

Glad to know I'm not the only one

Are you perhaps not starting in the correct runlevel ? What happens when you switch the runlevel.

I could be wrong though.

Regards
Marios

I have no idea which runlevel my PC boots into, will read on it.

Thank you, mariose.