I just installed Xubuntu 8.04 from a CD, finally configured it a lil'bit, but I have a strange issue

If I input the user and the pass then press Enter I'll end with a black screen. "Previous" doesn't work (there is a previous, see below).
If I input the user and the pass, select the session type as Xfce, then press Enter, it's Ok.

What happens and why? How can it be remedied?

Thanks

seems like somthing is wrong with session. What is the default session? Probably the one that is saved. To overwrite saved session go to sessions settings and save session.

I never saved any session, I had no idea that one needs to be saved...

I'll do this at home and see what happens...

A session doesn't need to be saved. What was meant, is that if you logged out of a KDE session, last time, say, then that option will be saved and presented to you, next time you go to log in. Same with a Gnome sessios, or what have you. It doesn't sound like you've had a successful login for anything other than Xfce, so far.

It sounds to me like you have a graphics problem, which is preventing anything more elaborate than Xfce rendering properly on screen. Is this black screen accompanied by a dark, X-shaped cursor pointer, wherever you move your mouse?

No, nothing at all. I said that I have no problems if before pressing Enter I choose Xfce as session. If I let it "Last session" it goes black.

The issue is not a problem for me but for my wife ... and it's somehow a problem

I said Xfce because this is all I tried (I knew Xfce is the default manager for Xubuntu).

Once more, this is a fresh installation of 8.04, I'm trying to learn ....

UPDATE:
Solved from itself today, but ran into another issue - I left the PC unattended and I found it in a sort of PowerSave situation - I couldn't get the screen back (the yellow LED turned Green - ie the monitor got signal - but the signal was "black").
So, how to get out of this situation and/or how to disable this behaviour?
I remember I had this issue once with 7.04 (or 7.10) but only once ....

UPDATE2: I opened the "Control Panel" and unselect the Power options (ACPI etc.). It worked for now.