Create or update the boot disk. Every Windows user should have a boot disk and every NT client should have an emergency repair disk. Check the operating system and applications. Update your OS and applications with the latest service packs or updates. Check the connections.
Users love to move their equipment around.
Make sure all the plugs are snug in their connections. And make sure you are using surge protectors and not a string of extension cords to power the machines. Make sure the hardware works. Many computers haven't seen a floppy or CD inserted in years as most upgrades and new installations are done from the server. Clean or replace floppy disk and CD drives as needed.