if you can't boot the phone I recomend that take off the battery then conect the usb to the cpu and the phone , on the n900 press the "u" in keyboard and then put the battery. finally run this comand

flasher-3.5 --disable-rd-mode -f -F RX-51_2009SE_3.2010.02-8_PR_COMBINED_MR0_ARM.bin --flash-only=kernel -R

this will return your phone to normality, from here you can try again