Current does not boot - BIOS problem?

Hello list,
Yesterday I upgraded to latest -CURRENT.Although the build and installing was successful, the system refuses to boot.It stops at the boot sequence with the following error:


Can't work out which disk we are booting from.
Guessed BIOS device 0xffffffff not found by probes, defaulting to disk0:

panic: free: guard1 fail _at_0x5195c from /home/ncvs/src/sys/boot/i386/loader/../../common/module.c:957
--> Press a key on the console to reboot <--


I cannot figure out what kind of problem is it.It's weird that the system cannot find which disk to boot from.I didn't have such problems at past and I run CURRENT at this desktop for over a year.Also I want to add that I cannot either boot the kernel.old , as it hangs when I try :
kernel /boot/kernel.old/kernel
at boot prompt.


If you have any ideas, you're welcome!

Thank you.

Ilias Marinos