Ok, I was pretty sure that the hardware issue with my N900 was a loose usb connector. I am now pretty sure that it isn't. Here are the symptoms:

• One evening there was a runaway mupen64 process in the background for about half an hour. My n900 was overclocked to 850Mhz. When I rebooted the phone it wouldn't boot up. I thought it was because of low battery. When I tried to charge it, the LED glowed yellow, and once every ~10sec the phone vibrated the led turned off for another ~10sec and then the yellow led turned on again.
• So I found someone who has the same battery and we recharged the battery and I plugged into my phone and turned it on. The nokia boot on screen showed and about 10 seconds later, the phone died leaving a faint nokia on the screen (backlight turned off, like it was connected to the PC)
• The usb port doesn't seem overly loose so I didn't think it was that.
• I don't think the n900 overheated as it was in the evening and I didn't notice it more hot then usual.
• It fall from my hands that week from not too high too a carpet and I didn't notice any damage.
• I don't think the CPU is fried since it shows the nokia logo
• It might be damage to the on board storage, but would that happen?
• It might be the USB connector sending screwy interrupts to the CPU but that seems unlikely.
• Any other ideas?

Note: I am sending it to repair by nokia in about a week, but I would like to try and recover my contact before hand. Also I am getting a bit worried that they will tell me that this isn't covered by the warranty.

looks like you need to reflash , oh and overclocked kernel VOIDed your warranty

It's been known for the EMMC to become dislodged from the boards of some N900s after being dropped.
Until you get it to boot there's not a lot you can do to find out what the problem is.

If you have a household contents insurance policy (not sure about these things in Israel), it may be covered for accidental damage.

Hi I had exactly the same problem with my N900 it would not boot up also I did drop it on concrete, i don’t think that caused it to fail and the other thing i never overclocked my n900 as HellFlyer said just reflash it and it should be fine.. Good Luck