Is it your personal computer? It sounds to me like a network administrator has setup the computers so that you can not change things (settings, backgrounds, etc...). This is normally only done at schools/offices, and if this is the case there is no way around it.
If you acquired this computer from a coporation or school it is possible this security was in place, and they simply did not remove it. If this is the case you will need to know the administrator password .
If you acquired this computer from a coporation or school it is possible this security was in place, and they simply did not remove it. If this is the case you will need to know the administrator password .