installation problems

[Murat SEVGİL]

Hi...Ive been using ubuntu for a few years....In the past I could use different desktop environments but now whenever i install a different desktop environment other than ubuntu after logging out the session and logging in with the other DE the screen begins to flicker and i cannot see the desktop .....you won't believe but ive been doing a clean,fresh install for 4 weeks now every week ..also when i logged in to cairo dock's DE the same thing happened......why can't i use both KDE and ubuntu together? I have a PC which has a 3GB RAM and an intel pentium chip....
And,another thing sometimes ubuntu keeps crashing so much...is there a keyboard command which will help like ctrl-alt-del in windows?Because when the computer is stuck and frozen i cannot help anything but reboot with the computer's power button?
Thanks,anyway...

[yancek]

but now whenever i install a different desktop environment other than ubuntu

Ubuntu isn't a Desktop environment it is an operating system.

.why can't i use both KDE and ubuntu together?

You can, it's called Kubuntu which is Ubuntu with the KDE desktop environment. You can also install KDE with a standard Ubuntu. I'm not really sure what the problem is? Also, the Ctrl+Alt+Del command should work on almost any hardware and isn't related to or specific to windows.

[grahammechanical]

May I add something?

When we install the latest version of Ubuntu or a member of the Ubuntu family of distributions we also get the latest video drivers and if a video adapter is old and if we are running on a proprietary video driver then it may be that the proprietary video no longer supports our video adapter. We need to use the legacy version of the proprietary video driver. This is the situation I am in.

Also, I have noticed that with Ubuntu 15.04 and using the open source video driver (Nouveau) on my older Nvidia adapter that I get GPU lock up and the screen freezes completely. I get this when I select a large amount of text in a Libreoffice document. Using the legacy Nvidia driver solves this problem.

When this freezing happens on your machine press Ctrl+Alt+F1 and see if GPU lock up is printed there.

Regards.