As you kind of suggest, sounds like a hardware issue.
Are you able to look at the Motherboard and associated cards physically by opening the case ?
My be the unlucky case of ageing components. Look for badly seated PCI boards, bulging capacitors, poor power connections.
Certainly worth cleaning out all the dust (especially from the fans), removing and reseating all connectors from the power supply and the same process for all cards. Leave the cover off and see the result.
Worth downloading a temperature utility to see what heat is like on hard drives and around the CPU - this is a good start :
PC Wizard
Unfortunately it doesn't give the core temperatures i.e. CPU temp. but can give some indications of what may be wrong.
While not an expert in HiJack I don't see anything there to be concerned about.