How do i fix this Windows 7 problem?

i got my dell, windows 7 laptop a little over 2 years ago, its been having this problem since about the 4 month having it. When ever i try to turn it on and get onto my account, the wallpaper and all my personal settings have been reset. An error box comes up at the bottom of my screen saying ive been logged onto the default profile and if i needed to fix it, i need to contact my administrator. Only problem is that is is a personal laptop,,, So that's one problem, another is something to do with my temporary files i think. Because every time i try to update or download something, for example, updating my iTunes, it gets fully downloaded but then an error box comes up saying that the temporary file is not found. I've checked over and over and made sure i have a temporary file, and trust me i do. What should i do? Should i just reset the whole thing and basically start over with this laptop? Help....