Network access database problem

The network has two servers and about 15-20 clients the clients only use one application everyday a bespoke app that has had no problems until recent server move all cables have been tested and changed switch has been changed various machines left of network for a few days all to no avail all network cards set to 100mb half duplex at end of tether trying to fathom out.Short of swapping out the servers which would be mu next step.