I was in Kindergarten in 1995, about the time I began to learn about programming from my kid's V-Tech laptop that came with a version of BASIC. My uncle gave me an old 286 laptop that booted DOS and QBASIC off of a floppy, and this was at a time when Windows 95 was out and on our home computer...
My 540C actually had its little "PowerBook 540C" badge replaced with "PowerPC" so I'm thinking it used to have an official Apple PPC upgrade. Unfortunately, it's just 68k still :p
My hinge was fairly strong until my cats knocked it over while playing, and now it's a bit loose and part of the side chipped off. I plan to superglue it, but it still sucks! Try closing it with care as someone else said above, that will keep it from recieving too much stress.
I've had three 500s (my first was when I was about 12 or so) and I believe it's a loose socket on the PowerBook. My current 540C has this problem. It works well enough that you can move it around with care, but if you snag it the wrong way it shuts off. You can probably strengthen it by...
The 500 series is fantastic. I have a 540C that I purchased from eBay for about $25 with a massive 36MB of RAM. It runs CodeWarrior, RealBASIC, Photoshop, Netscape... It's fantastic. And it runs OS 8.1 just fine. In my opinion, this is the 68k PowerBook to have!