you can only boot your hard disk with same configuration of hardware on to you have installed that OS.
Example:- suppose you have a dell optiplex 990 desktop and you have installed win 7 on to the desktop. if you remove the hard disk from optiplex 990 and install it to another optiplex 990, than it will boot properly with no errors or crashing reports, but you install that hard drive in another desktop or laptop which is different in model, that time you will face errors and crashing reports.
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