Black screen, Flashing white line

if you check the microsoft website for OS help, they HIGHLY reccomend that any time you do any major changes to your computer's hard drive, that you do a fresh install of windows. this ensures that your copy of windows will indeed, work. since each computer's specs are as different as human beings, it makes sense that it wouldnt fire up. also, remember that when you install a new part on windows, it takes a while to install the necessary drivers for that individual part. and since you posted that you took a HDD out of some other comp and jammed it into the one in question, my best guess is that it locked up the OS with driver file installations. bottom line, reinstall windows FRESH on the comp with the prob.