Generally speaking when you switch hard drives, if the new drive has an OS on it, it will not boot. You'll need to format and reinstall an OS after putting the new drive in the PC.
I think it's possible to get around this but I'm not completely sure how.
Anywhow, we need a little more information than what you've provided here.
The procedure for removing and replacing a hard drive in a Dell computer, for instance, is different than it would be for a personally built PC.
Generally the procedure involves unscrewing the hard drive from the case (it might be attached to a bin that removes from the case as well), unplugging the drive from the connector on the motherboard and the data and power connectors on the drive itself, screwing a new drive into place, and attaching the data and power cables.
Afterward you need to set it up in Disk Management in Windows.
But the specifics of that might differ depending on what exactly we're talking about, and whether we're talking about a boot drive or not.
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