Would swapping a hard drive into another computer cause problems?
Yes it will and it’s because the OS installed on the hard drive does not recognise the Motherboard, the CPU, the BIOS on the board and the video card. Therefore it does not have the correct drives for them to boot. If you have an installation disc for that OS just put it in the CD drive and reboot and it will find the set up disc. While it is installing it will install the correct basic drivers for the new system. However before you do that put the drive back in the old computer and back off everything you want to keep or you will lose it all.