|Nothing in the server logs that the server restarted unexpectantly?|
Nothing in the workstation event viewer logs?
Switches/server on ups's?
How are you mapping the drives?
When there are red x's on the drive mapping can you browse to the server shares via Network?
There has to be a clue somewhere.
You may wish to review this thread. Ignore the last entry since the guys issue is he has no dns name resolution which is why he had to use an ip address instead of server name