Woo woo, I'm now 6 for 6 on repairing the "broken" Cricuts I got off eBay. (ok, Danny M. gets 95% of the credit for the one with the busted middle-layer board traces)
The last holdout was a Personal model, which would beep three times when powered up. Nothing from the LCD, all the keyboard lights would come on.
I started by plugging a known-good power supply into it, just in case, but it didn't make any difference.
Next, I removed the bottom cover where the motherboard lives, and immediately spotted the culprit. The LCD header was unplugged.
After plugging it back in and powering it back up, angels sang, it started right up and gave me the "Cricut 1.0 OK"!
Incidentally, I had been wondering if the earliest firmware versions had perhaps not been read-only, so I plugged in my handy programmer card and attempted to download the firmware.
At first I thought I had hit paydirt, the file was NOT all 0s like the others, but alas, I realized the bytes were all sequential numbers in an interesting pattern (high-byte increasing across, low byte increasing downwards).
This machine looks pretty much unused and gleaming. I wonder if it was bad right from the factory? How else could a header just come unplugged like that?