Some do take proprietary supplies. pcpowerandcooling.com and other vendors have replacements. Even Compaq sells such things. But you have to pull the plug if the financials don't make sense. The hard disks are rarely proprietary since its far too costly to make such a custom item.
Bob
I have I "Compaq Presario 5600" that needs the hard drive and power supply replaced. Does anybody know if these are proprietary items. I noticed that the motherboard has an additional pwr. supply connection in addition to the 2 standard connectors.
Thanks in advance
Jerry

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic