R.E.I.S.U.B. reboot your system
From PCLinuxOShelp Knowledge Base
When all else fails, don't pull that power cord just yet. So when you are at your wits end and your computer seems to be locked up. There still might be a way to recover without just pushing the power button or just yanking the power plug. Here is what you need to do. This will work in 95% of all cases, where you computer appears to be totally locked up. This will not work if you have had a kernel crash.
Just remember this simple phrase Raising Elephants Is So Utterly Boring.
Holding down the Alt and SysRq (which is the Print Screen key) while slowly typing REISUB will get your machine safely restarted.
So what does this phrase do exactly.
R: Switch the keyboard from raw mode to XLATE mode E: Send the SIGTERM signal to all processes except init I: Send the SIGKILL signal to all processes except init S: Sync all mounted filesystems U: Remount all mounted filesystems in read-only mode B: Immediately reboot the system, without unmounting partitions or syncing