when you say you "reinstalled one of the machines", you mean that you reformatted/reimaged the whole machine.
Most likely, the machine hasn't actually recieved the SMS Client yet.
Check the Problem machine, Control Panel, does it have the Systems Management tool?
Did you create the machine with the same name, IP? If so your best bet is to remove the current entry for that machine in SMS. More on that if we need to.
Make sure you have configured your discovery settings, and increase them to rerun more regularly, just temporarily, while you redect this machine, and force a Active Directory Systems Discovery.
Don't forget...to see discovered/net details of object in collections you have to right click on the collection > all tasks > Update Collection > Update Sub Collections, then move to the right hand panel, right click and refresh.
A refresh wont update from the database, and an update collection wont automatically update the machine list view.
Lets know how you get on with those lot.
Hope this Helps.
Neil J Cotton
njc Information Systems
Systems Consultant