Thanks guys your replys helped me a lot.
The problem was my n900 could not boot the OS hence neither the wall charger nor the USB cable could charge the N900 battery.So i bought a universal charger for mobile batteries and charged the battery and it worked.First i did was rescued my data by using Rescue Initrd(http://wiki.meego.com/ARM/N900/Using_Rescue_Initrd) .Then flashed only the kernel by using --flash-only function of flasher (flasher-3.5 -f --flash-only=kernel -R -F <firmware-image>).. and it was done..
thanks once again...


(@geneven Mumbai, one of the unique cities in the world, glad that you have been interested in it)