Network Errors

[XxGodJrxX]

I am at work right now, which is a small office where I am the only one that is REALLY computer literate. The problem is that we cannot access each others' computers through the networks all of a sudden. The internet is still working, and yet we can't get to each others' computer. One of the computers also has a box opening up saying "enter network password", which keeps popping up with the username and password already entered. I do not know why the networking password is not being allowed, why it keeps popping up, or why this problem has popped up all of a sudden.

All of the shortcuts to the other computers on my machine have disappeared for whatever reason. On the other computer, the error message reads that access is denied. Any help would be highly appreciated.