Every Windows user should have a boot disk and every NT client should have an emergency repair disk. While you're making your rounds, poll your users and make sure they have the disks they'd need in case of an emergency. 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 your users are using surge protectors and not a string of extension cords to power their machines. While the computer is open, re-seat all connections including expansion cards, CPU, memory, data cables and power connections. You'd be surprised how often an expansion card isn't seated all the way, especially AGP video cards and PCI cards. Update your master inventory of computer assets.