Ok, I'm having a similar problem with my twelvfth Express. Built the unit, power test - good lights on 3.3v and 5v leds. Installed the chips, wired it up. I installed a PIC plugged in: 3.3V led and 5V led lit. LED #5 lit as well.
I had this problem in previous builds. I unplugged, attached myPickit2, powered up, Ran PICkit 2 v2.61, erased the memory on the PIC, Black Check. Loaded LE_Firmware_09_2010.hex, Write to PIC, Verify. All ok. (I know I'm doing this right because I did it the same way for my eleventh build 2 minutes earlier).
I remove the Pickit2, repower and I get the following:
3.3v led lit, 5v led lit. No startup message. LED display numerals are blank.
I power down, remove the numeral displays and the adjacent chip. Verify pins not bent and reinstall. I remove the board from the case, flip, and painstakingly check every solder joing for bridging or poor contact with the board. No obvious problems.
At this point, I'm open to suggestions... anyone?