Can't tell if I have been hacked :(

[Lovell Mcilwain]

Hey guys,

Can you give me some input on whether I have been hacked or not?

I logged into my machine via ssh and found that I couldn't run any 
commands and got a input/output error.  I couldn't run the who command 
to see if anyone else was logged into my machine and I couldn't check my 
firestarter log to see if I have been breached.

I was able to run an ls -al and found that a lot of my permissions had 
???? as the owner.  My gnome interface is pretty much disappeared and 
all I see is the background.  I can't shut down this machine because the 
halt and shutdown commands are not recognized (I get the same 
input/output error)

Is it possible I have been hacked?

If so how is this possible when I have set my firestarter firewall to 
only allow connections from a specific network address and to deny 
anyone else that tries to connect?

Any input is helpful.

Thanks