When is it time to retire old technology?

I've spent the better part of this afternoon ripping apart my parent's laptop to replace a hard drive in it. The hard drive cost me $100 and I have a feeling it's only a matter of time until something else decides to fail on the laptop. Perhaps the motherboard is next...

In any case, how long is it before upgrades no longer make sense and it's time to drop $2000 on a new laptop. They do still cost $2000 don't they?? (Goes to find out you can get a brand new one for approximately $800).

On a sidebar, here's the manual that I used to crack it open: Compaq Presario 1600XL Service Guide.

I'll need it again when I put it back together... And yes, I know it's an ancient hunk of a laptop!