crash a computer

There is a program available called Darik's Boot and Nuke that you can download and copy to either a CD or floppy that will completely wipe the contents of your hard drive. You can download it from http://dban.sourceforge.net/ I've used this program in the past to wipe drives that used to be in medical offices for compliance with HIPPA, and never had any problems with data coming back.

what exactly happens? can you still load your operating system? can you provide more details?

I guess you mean by force shutdown ... if your systems hangs there is no way to force shutdown rather than resetting the system