Question install o/s

[Drummers1]

i have windows 7 on my pc, i also have a spare hard drive so i put that in and tried to install windows 10 on it, i ran into problems with that so i went to put the windows 7 hard drive back in but now it wont boot up, have i done something wrong ?

 

[richiestang_78]

Go into your BIOS and be sure the correct drive is selected as the boot drive.