How can I perform an Apple Hardware Test without my original install media?
Solution 1:
I've never been able to figure out why this function seems so unreliable - holding D for diagnostics doesn't seem to work for me in practice. I wish I had a better explanation than "many models don't have this and even the ones that do, this isn't something I can count on."
I have come to rely on AHT that are available for authorized Apple technicians to download so you might be able to get help from one closer than an Apple Store - http://www.apple.com/buy/locator/service/
Apple will usually run a very good test for free as past of a genius bar appointment, and both Apple and Authorized Service will usually check a mac in for diagnostics under coverage for no charge. Out of warranty, expect to pay $39 to $85 for a diagnostic.
Lastly, you can order replacement media if yours are misplaced from Apple. 800-APL-CARE
Solution 2:
The only thing you can do with the Snow Leopard disk is to boot to it by holding "C". You could also hold down the option key and pick the disc to boot off of.
Then you can go to the Utilities Menu>Disk Utility and run "Verify/Repair Permissions" and "Verify/Repair Disk". One or both of these tests may yield some information.