It could be one of many reasons that it dried up.

If the temp has been very hot or cold the grass can go dormant.
It could be pests, bugs, etc.
The soil might not be able to sustain a lawn anymore, if it's very hard packed, or lacks nutrients etc..
It could have had a fertilizer (or other product) spread on it improperly, therefore burning it and killing it.

If you could provide some more details on soil conditions, recent activity/work on the lawn, weather conditions, anything out of the ordinary etc.. it might be easier to pinpoint the problem.