My computer asks me to run a Manual FSCK

[Dr. Noah M. Hastings]

I use to have an  X-Win environment, but don't anymore.  When I first bootup my system, I the the following error:
/dev/ad4s1a: CAN'T CHECK FILE SYSTEM.
/dev/ad4s1a: UNEXPECTED INCONSISTENCY; RUN fsck MANUALLY.
Automatic file system check failed... help!

How do I run a manual fsck?  
I have tried fsck -f, which is a force, a fsck -p and still nothing.  I am sure there is a way to repair my installation?

Need all the help I can get.