Suddenly cannot access network drive

For at least 2 years I have been able to access the C drive on my main
computer from the other 2 computers in my home network (one wireless,
one ethernet). Suddenly, I get a message listing the IP address
\sharename of the drive and aying that the network path was not found.


I have done an IPCONFIG /ALL on the base computer and verified that
the IP address has not changed (it is a static IP). I also verified
that Microsoft File Sharing is still installed in the LAN connection
for the base computer and that the C drive is still shown as being
shared. In an attempt to fix this, I turned sharing off for the drive
and then back on, but I still cannot access it from the other
computers. I did a Net Use from one of the other computers and it
shows:
Unavailable Y: \\192.168.1.104\XPS400C

What could have caused this to happen all of a sudden and more
importnatly, what do I need to do to get it to work again?

I couldn't seem to find any recent search hits on this forum.