Vista problem ( log-in)

I have had my dell insp 530s for only 4 weeks , and when i tried to log on to vista it would not let me. I had the password correct and made sure CAPs were not on. Even still it would load.. then say somthing like Windows has an error and just log me back off? I called dell/bestbuy, and they said sometimes a file for vista gets damaged and i would have to bring it in for them to fix (29.00$) So instead i just rebooted the whole thing over and its working fine again.
My questions are .. have anybody else had this problem ? How do you fix or prevent this?