shouldn't matter that its a dell. I assume you're clicking on highlighted dates in the calendar, so I'd double check the alloted space for backups on the monitoring tab, make sure the system restore service is running and set on automatic, if she has service pack 2, make sure (slim chance) DEP on the advanced tab of system properties>performance>settings > data execution properties hasn't added the service.....

boot to safe mode and try to run restore from there. Other than that, I can't think of anything, or than corrupt restore points. Delete them all and create a new one and try to run it.