Why did plugging a another HD is to PC Cause other HD to fail?

Arterus

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Oct 16, 2009
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My girlfriends laptop messed up, so I went into the bios and ran the diagnostics and the error code it gave me was missing boot manager. I wanted to see if I could just connect her HD into my working desktop and format it and reinstall windows for her. But when I powered my desktop down, plugged in the hd and powered it on. My computer loads then says missing boot manager press ctlr+alt+delete! So I just powered it down and then unplugged her hd from my desktop. Then when I powered my Desktop back on it still says boot manager missing. I have spare hardrives and it was just my gaming pc and not my work pc. So not a big worry. But why did that happen? I thought my pc would boot like normal and just read the other hd or not read it at all. I didn't think it would mess up my boot manager. Any ideas why?

Nevermind, my pc finally booted normally. Im guessing my pc tried to boot her hd first and then saw the boot manager was missing and when I powered down and unplugged her hd, My pc still had it stored in the virtual memory as her hd. Its running solid now.