If you hold the power button in for 5 seconds, the unit should power off without the need to pull the power cord.

Can you start your computer in safe mode?  If so, you have a driver or system program that is mis-behaving.  If this is not Vista, you can use msconfig to disable the startup processes until you find the one that is causing the problem.

If you still have trouble, give us more information; ie, what operating system are you using?  Did you update or install anything lately just before the system started hanging when you boot it up?

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