Nokia N800 seem to have similar partitioning w/ N770. From the look of it /dev/mtdblock4, means the flash have atleast 4 partitions. being partition 4=rootfs(compressed). The other 3 probably are, loader,debug/flash mode, and may be the kernel. saying that you was able to reflash it, then probably means the 3rd or 4th partition is corrupted. Why not try reflashing it w/ developer kernel, rebooted and reflash it again w/ the normal kernel.