File Server file access is Slowwwww

We have a file server using NT 4.0 SP6a. We recently started having problems accessing shared files on this server from all workstations. Files are loading extremely slow. I am running performance monitor and it is showing 100% all the time on server\total files opened. The counters for Server Work Queues\Bytes Trans. per second; Write Oper. per second; write bytes per second; and bytes sent per second are peaking to 100% frequently. I am not sure what these counters are telling me. Can anyone tell me what they mean, and how I should try to alleviate the problem?