You won't believe this but...
I also had the inspiron 1100 not turning on problem. I ALSO was wondering about the lid switch being as the thing had died such a quiet death while sitting quietly in a laptop bag in my office. But alas, no lid switch to be found.
After reading this thread, I thought hmmm, what's the chances that if I break this puppy open and accidentally jam a flathead screwdriver through the CPU, the network admin at work will be happy with me having taken the initiative in the repair and promptly order me a new notebook?
The chances of that seemed slim so I came up with an alternate plan. Figured out where the latch magnet switch must be by sticking a screw to the magnet above the lcd and closing the lid, went down to my cellar, grabbed a rare earth magnet I had farmed out of a dead hard drive long ago, and held it above the switch. Wallllar, she boots!!!
Funny thing is, we had 2 Dell notebooks at my last job with exactly the same issue, and both were considered DOA and stripped LMAO