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When you change a hard drive frome on PC to another, you will have trouble unless you prepare for the move. Your hard drive in PC1 is set up with information from the hardware in that computer, and when you switch it to PC2, it's as confused as Britney Spears onstage at the VMAs. First off, it's hard to move an established copy of windows to new hardware, but not impossible. It's best to format the drive and start fresh if you have the means. If you don't want to format, at least back up all critical files or better yet, obtain an image of the drive before you mess with it.
I suggest you hook up the drive that's hanging at the windows boot to your other working computer, set it as a slave drive and copy your critical files to that drive. Once you do that, format that drive, and reinstall windows, then put in your critical files and start fresh.
If you don't want to do that, just before you shut down the hard drive you want to move, uninstall all the hardware drivers you can find (don't do this unless you have the motherboard CD AND your windows CD!!) and pop it in the other machine. It'll ask you for drivers and it might work once they're installed.
Again, it's a crapshoot if you want to change established copies of XP to other machines, and I HIGHLY suggest you don't attempt unless you have a clone of the copy you don't want to lose! I
can't stress enough the very real possibility of you losing all your data, so please don't attempt if you don't have the knowledge.
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