can you tell me what are the correct commands in mandriva and ubuntu to install a driver?also how to stop and start the x server?
First of all, Mandriva provides Nvidia drivers in the packaging system, from MCC, install software, you should be able to find them. You can install packages in Mandriva, with 'urpmi nameofpackage' or use the GUI in MCC. If you install drivers from Nvidia, you are on your own. Nvidia drivers are binary files. I use them on my Slackware system. You make them executable, and run the installer. The installer does the rest. I can not tell you about Ubuntu, my Ubuntu is on a netbook and does not have an accelerated GPU. So the standard drivers work out of the box. As a guess, Ubuntu will supply packages like Mandirva. Use their packages, not the ones from Nvidia.
The init systems are different on Mandriva and Ubuntu. I don't know the levels, you will have to look into that yourself. I no longer run Mandriva, I did for 6 years, gave up when it was sold to Russian interests. I now run Magia, as a backup system to my Slackware system.
You can start the x system on most systems with the command 'startx'. That can be run as root, or as the user. To restart x, the hot key combination of Ctrl + Alt + Backspace will restart it on most systems.
If it fails to start, look in /var/log/Xorg.0.log for any errors that may occur. That is the best starting point.
now i have installed Ubuntu and i followed the same procedure in Ubuntu to install the driver,and they installed correctly,and i was able to get 1920x1080 res earlier,but on the next day the same thing happened,it displayed a black screen with a prompt.every time i boot,i only get a black screen with prompt.is there any way to solve this?
This sounds like X is not being started on a boot. You need to know what init run level it should start in for X to start up. Is it in the correct run level?
What happens if you do a 'startx' command ?
Run 'lspci' as root, it may not be in the path of the regular user. I also do not know where they put it on your systems.
If you what to find it, you can use the find command, or, run the command as root, 'updatedb'. That takes a few minutes on a new system. Once the database is built, you use the command 'locate filename' to locate what you want. It is much faster than find.
Firmware not found, is not good. You need to know what hardware needs it. If it is not in the packaging system, then you go to the manufactures web site and get it from there. Wireless cards often need firmware. What ever needs it will not be working, or not working at its best.
As root, run the command 'dmesg' and look through the boot messages for errors. That may give you a clew on the firmware.