The black page that pops up is a called a "kernal panic event", a message sent by the computer to warn you that there's a software or hardware probleme occuring. It could be a lot of issues but in your case if you still have the machine original hard drive from 2005 I would suspect it to be the culprit but I could be wrong. Does it always happens when using the same application or do you feel the computer is overheating ? Ram issue ?