Most likely, the flash contents was corrupted by accident. Try Flash recovery utility to see if it helps.
It's reported that this utility needs the serial cable disconnected during the operation.
# make modules_install INSTALL_MOD_PATH=/home/oskfs Warning: you may need to install module-init-tools See http://www.codemonkey.org.uk/docs/post-halloween-2.6.txt INSTALL net/packet/af_packet.ko ... not for this architecture make: *** [_modinst_post] Error 1
You might need to change the kernel Makefile as well, to point the new depmod, usually in /usr/local/sbin, not /sbin.
The OSK machine id was assigned after the OSK hits the market, thus the OSK keeps to contain old machine id (212) as manufacturing default, while newly built kernel has correct one (515). As the pre-build bootloder expects the old value, the newly built kernel doesn't start.
You can either a) download the latest u-boot, or b) use the old machine id in your kernel with the instruction below.
Add the following lines in linux/arch/arm/boot/compressed/Makefile
ifeq ($(CONFIG_ARCH_OMAP),y) OBJS += head-omap.o endif
Add the following lines in linux/arch/arm/boot/compressed/head-omap.S
#ifdef CONFIG_MACH_OMAP_OSK
/* support for booting without u-boot */
mov r7, #(MACH_TYPE_OMAP_OSK & ~0xf)
orr r7, r7, #(MACH_TYPE_OMAP_OSK & 0xf)
#endif