Two days ago, I formatted a supposedly unused partition via Windows XP. I think that corrupted my freebsd boot manager. I'm not able to boot into freebsd now. I get the following error:

mounting root from ad4s3a
setrootbyname: failed
ffs_mountroot: can't find rootvp

Manual root filesystem specification:
<fstype>:<device> Mount <device> using filesystem <fstype>

e.g. ufs:/dev/da0s1a
? List valid diskboot devices
<empty line> Abort manual input

When I type:

ufs: ad4s2

I was able to boot into freebsd as root. But I have no idea how to fix the problem.

Could someone please help

Thanks in anticipation