How can I login as root on kde? If I logout, I cant see root, and just I can see my name as user. I know how to login on console but not on kde. thanks

This question is very confusing to me. If I understand your question right.

In kdm or gdm use username = root and password = <root password> but I do not see many reason to login to kde as root unless I took Michael Robertson of Linspire's points or I forgot the terminal commands to add users and had to log in as root to access the gui.

Maybe you are using a login manager/theme that only has users pictures and you can only type a password like the default in windows XP. In that case, I would go to the control panel and switch login manager themes in order to be able to enter usernames by typing them in.

Because I have installed usb stick but if I am not root, I cant access it. I want to access it on desktop but I cant.

You can access it as user as long as you mount the usbdisk correcty. Maybe you can even change the permissions after you mount it but am not sure. Hopefully somebody on LQ can confirm this. After you mount to change the permissions I would try a chmod 755 /dev/sda1 or wherever it is mounted.

I am using sda1 in this example but I dont know what your usbdisk is mounted under, dmesg should tell you.

To mount it and have non-root access to it try as root from terminal.

man mount

for a better understanding of how this works or check out this webpage
http://www.tuxfiles.org/linuxhelp/fstab.html

I have tried and it works thanks

The /etc/fstab file is also important in understanding how mount works.

Remember that Linux is designed to put the system administrator (which happens to be "you") in control. It does not trust its users, and does not give them much authority. You decide what ordinary users (such as yourself, most of the time) can do. And this is such an example.

You can decide that "ordinary users may mount this USB-device." You can decide whether or not the system should allow programs to be executed from that device. You can decide whether the files on the device "belong to" the user who mounted the device, or if they may be shared by other system users. These are the sorts of things that you, as "root," have the authority to specify, by means of the fstab file.

Incidentally, you should set up your ordinary user-account as being "limited" in this way... do not use the computer "routinely" as root. These "inconveniences" are there to protect you...

In the /etc/fstab if you wish to have regular users mount the flash drive you need to tell it to, append the /dev/sda* line with the users command
mine looks like this
After you add it to the /etc/fstab, all you have to do to mount it is open a console and type mount /dev/sda1

Newer versions of KDM (KDE's login program) don't allow a user to log in through root in KDM.