MacBook Pro 17" internal HD failure?

I have just bought a june 2009 model 17" 2.8GH . The previous owner had upgraded to 10.8 and then appeared to have done a bad erase of her data. We changed password OK. Then I found no apps or utilities worked, just red in menu. No way of using 10.8 restore without her password on app store, but I didn't want it anyway

But the OS10.6 Install disc would'nt work, just alternated Apple/no entry sign/question mark.

It worked fine off the Super-duper bootable back-up from my old 2008 MBP 15. So I erased the whole HD, including restore partition using disk utility. Then using Super-duper, I copied the whole back to the internal HD & it booted up from the internal HD fine.

After running faultlessly for about 4 hours, it froze (in DxO optics) & would not re-start from internal HD. After various attempts, the situation remained that it runs from external HD, but not internal. The hardware test short and full (1hr 17mins) showed no faults. Meanwhile the internal HD gradually first reverted from my name to 'untitled' then totally disappeared from disk uitiliy, choose start-up disc icons & super-duper copy option.

Looks like the internal drive was on the blink/brink and I have pushed it over. But before I order a new one (WD blue 500 5400rpm in mind)....is there anything else tat could cause this behaviour?