Installing a new Hard Drive

Hi all, i recently scraped an old computer i had laying around in my house, and i salvaged the the hard drive. I would like to install the hard drive in my current computer for a little extra space. But there is one thing i am not sure about which is that the old HDD as an OS installed on it. If i install the hard drive and boot up my PC will the second OS affect the boot up and also try to be booted up simultaneously? And once i have the new hard drive installed can i wipe in clean from my computer?

Thanks,

Scott 

No it shouldn't be an issue. Just open up your boot priority menu on start of it does and select the drive with your primary OS on it. 

Then once in the OS just format the other drive. 

Thanks man really helps me out :)

You shouldn't even have to do that, the main boot drive will remain the same, just stick it in the system, boot up the computer, and format the new drive.