PC sometimes not shutting down/rebooting correctly
I have an issue on my recent Linux Mint 14 KDE mint4win installation (had it ever since the installation was fresh): sometimes when I turn my computer off or reboot it (both normally, of course, via the KDE menu) it will not turn off or reboot, but instead freeze with the black screen and the KDE mouse cursor on top of it (which can't be moved). In some cases, however, the PC will turn off/reboot normally. When the PC freezes, sometimes doing Ctrl+Alt+Backspace helps to kill the X server and then try the shutdown/reboot procedure again (in that case the second attempt is usually successful). Sometimes, Ctrl+Alt+Backspace doesn't work (and neither does something like Ctrl+Alt+F1/F2/etc. to switch to another virtual terminal). If that is the case, only the SysRq magic keys help to reboot the PC after which I'm able to try the shutdown procedure again once the system boots up. Can you please help me fix this issue? I'm rather new to Linux so I don't know what information would be helpful in this particular case - please let me know what logs and what other data may be helpful in discerning the issue and fixing it. Thank you very much in advance.