ouch!
same thing happened with me!
after that i dropped my n900 on the floor it started to reboot, but unlike you neither the battery nor the sim card popped out!
the phone kept restarting (for about 5 minutes) and then shut down with an error message.
what i did is that i sent it to nokia care, apparently what they have done is that they re flashed my n900 which solved the rebooting problem but another problem came in, the internal mmc card was not found by the n900!
so i resent it to nokia care and they said that it cannot be fixed!
so i was left with a bricked phone... i couldn't open the camera application or any other application because there was not enough memory, i couldn't even send sms or add new contacts to my phone!
what i did is i searched the net for a solution and i found that you can make your sd card work as a swap memory so i got an 8gb memory and formated it on linux (ubuntu) made 1 gb swap memory and the rest as normal memory and i installed rootsh on the phone and then activated the swap on to the sd card from the x terminal..
my only problem now is that i cannot install new applications on the phone or new themes and every time i restart the phone i have to go to the x terminal and repeat the swap on process!
i hope that you don't have a bricked mmc like i do but if you do this is your only solution...