Is there any keyboard shortcut for the "task manager" (like Alt+Ctrl+Del in windows) when my machine goes into a crashed state?
I am going to assume by "my machine go into crashed state" you mean that whatever task is taking up the display you are looking at has stopped responding. (In general, when something crashes on Linux, only that thing crashes and everything else keeps running. It's very rare that the entire machine comes to a halt.)
When all else fails, I like to switch back to a standard terminal interface (text mode as opposed to GUI) by hitting CTRL+Alt+F1. This brings up a login prompt. I then login, and enter the command
top to see what is running. The process at the top of the list is the one using the most CPU and usually the problem, so I kill it by pressing k, and entering the process ID (the numbers on the left). I then go back to the GUI by pressing CTRL+Alt+F7 (or sometimes CTRL+Alt+F8, one of those two will work, but it might change). If things are now working, I continue on, if not, I'll try again or may just force a reboot.
It's slightly related, but if you're dealing with a crashed system, you might want to invoke the Magic Sysrq key. This way you can kill all processes, sync your disks, print out the active tasks, initiate a crash dump, and much more.
You can also use xbindkeys and define a binding to pop up top, htop, *top, gnome-system-monitor, etc. Switching to a TTY (jwernerny's answer) is probably the best idea if your system or X server is acting up.
Just two steps:
Step1 : Type
top command in terminal.
$ sudo -s
[sudo] password for username : (type your password here)
It will give the list of processes running with process id , name , time , memory usage etc.
Step2 : Find the particular process and then it's respective id.Let us assume the process id as 12043 , then command goes like this
$ kill 12043
kill we can kill/stop/abort a running process/hanged process.