From failed motherboard, HDD to a blown OS. Before I work on such I ask the owner if there are any files at risk. If there are we clone the drive and install the clone so we leave the owners drive untouched.

Then I unplug all USB things, remove power and give all cables and boards a gently shove home. Then retry. If that hangs up we try getting to the BIOS screen what we do next depends on that result.