A few seeks ago my mac-mini 1.6 Intel Dual-core quit because the hard drive became full, logs downloads,etc. So I needed to reset PRAM and pretty well everything else as well, to regain boot up.
Whilst it is all fairly simple in theory, one point I had forgotten about since the last time this happened, was that the Apple flat alloy keyboard does not register the correct keypresses as it's driver is lost during the process.
So you need to hide an older keyboard someplace handy to do the revival keypress sequence.I kicked myself when I realised that my attempts were futile until I connected the bulkier keyboard from the downstairs iMac 17"(the one with the varicoloured horizontal lines on the screen, guess which batch this is from!).
All went well after this and the mini revived and is great since. Using Spring Cleaning app is useful in freeing up space on HD and I also managed to move all the iTunes stuff onto an external drive following Apple how-to's.