Anyone with NT experience???

I have a strange issue happening with my domain.

I have to restart my domain server nearly daily for the following reason.

PC’s that are logged into the domain suddenly can’t see the workgroup,
but PC’s that are not on the domain can see the workgroup.
Also when this issue arises the domain server can see the workgroup.

We noticed this when a user who had a mapped drive on his PC (on the domain) couldn’t access the drive (which is also on a PC on the domain.

Any ideas?? Anyone willing to help me figure this out??

Any help is appreciated.