Experiencing severe slowdown

Help!!

We are running a 5.0 network. Some users are experiencing a significant slowdown when accessing files in one section of the Network. These are heavy duty excel files (tons of fancy macros)that were working well on Friday.

We have eliminated workstation (NT)and protocal, switch and patch frame ssues. Nothing has been added to the Network prior to the slowdown. The volume has been purged (we’re running @36% capacity)

What have I missed????!!

Thanks for your responses.