Using my old HD with new computer

So, the power supply on my old dell Inspiron 8400 bit the dust and they don't make them anymore so I can't replace it. Someone I work with happened to be getting rid of his working Inspiron 531. My hard drive is better than his though and I want to transfer it over and use it to run the new computer. I put it in but it won't boot, it tells me I have to repair it but it won't do it when I try. What do I have to do to make this work?
 
You changed motherboard/CPU, so Windows won't boot. The easy way would be to just back up everything on HDD, wipe it, install Windows again.
 
I would do that but when I boot off the HD in the new computer with my old one plugged in as a secondary one the computer can't see it for some reason
 
Hey Ruthie. If the hard drive in your dead system is indeed good, you can buy the appropriate type of disk drive enclosure ( around $20), mount the drive in it, and connect it to the working pc's USB port. Depending on how much info is on your drive that you want to save, maybe you can burn it to DVD ( always a good idea for stuff you don't want to lose). Then, depending on which drive you want to use, format the drive and reinstall Windows and the drivers for the Inspiron 531 and either keep the second drive in the enclosure or configure and mount (then format it) in the desktop for additional storage.
 
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