You generally don't swap hard drives between PC's when troubleshooting the monitor.
When a MONITOR isn't working, the troubleshooting is this:
Try a different PC with monitor.
If the monitor works, the problem is the PC.
At this point, it's more difficult:
1. Does the PC even turn on?
2. If it turns on, is there an internal graphics card you can swap?
*There's not enough information provided for us to help. However, your model probably had both INTEGRATED graphics as well as addon graphic card options.
I also don't understand what you mean when you say "the PC checked out okay... the monitor wasn't working." ??? Was the monitor working with the other PC or not? If not, how did the other PC "check out"? So I'm a little confused here.