I recently acquired a Powerbook 520. It has a 160MB HDD and just the onboard 4MB of RAM. I managed to find a power supply for it and it booted up just fine. I got the flashing folder so wasn't sure whether the HD was dead, wiped clean or otherwise corrupted. While I went looking for a Sys 7 floppy to check, the PB switched itself off. I couldn't get it to start again. I stripped the machne and checked for damage or loose connections. Everything seemed fine but it still wouldn't boot or even chime. Fast forward a week and I was about to put it away as a bad job and gave it one more try. It booted up and this time the HD started up. It had an installation of Sys 7.1, Word, WordPerfect and a couple more applications. After about five more minutes it switched itself off again and I could not get it to restart. No chime or chimes of death. Nada. Not really sure how to troubleshoot this one. Clearly, the logic board and psu are relatively ok as the PB would never have booted otherwise. The heatsink over the cpu daughterboard seems to be fitting correctly, so I don't think the unit is overheating. I dunno.