Switching OS from HDD to SSD

Dec 20, 2018
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I have recently bought an ssd for my already used computer to download windows onto. I backed up 400 gb from my hdd into an external hard drive and then removed both to boot up using my ssd only. Now that I have windows downloaded, I'm wondering if there is going to be a problem connecting my hdd back. Do the two operating systems conflict? If so, is there a way to extract the data from my hdd?