In the first instance you should check the manuals supplied with your software.
If you have been running software and the system freezes. Step through the following
the procedures;
Press [ESC], if this fails try
[Ctrl]+[Break], if this fails try
[Ctrl]+[C], if this fails
check if all connections are still Ok, if all this fails ...
warm boot
Hold the [Ctrl] and [Alt] keys then tap [Del]. If that fails ...
cold boot
Turn off the computer - wait 20 seconds then turn on again.
DOS
Bad command or file name:
Spelling mistake in command line, file not in path/directory, not an exe, com or bat file.
Access denied:
Attempting to delete a file marked read only, or not owned by you (on a network), or
trying to delete a file opened in another application.