Toshiba Satellite A665-S6067 Fluctuating Low Screen Resolution

I brought a Toshiba Satellite A665-S6067 last summer. My problem with this laptop was the screen resolution. The screen resolution was set to the recommended in the control panel, which is 1366 x 768. When I accessed the internet, the screen resolution was set lower than what was set in the control panel. My screen resolution fluctuated almost every day. The low screen resolution made it hard for me to browse the internet. I had difficulty accessing Yahoo Mail, forums, and downloading desktop backgrounds. I have called Toshiba for technical support and downloaded drivers. Right now, my computer is at Toshiba, and they cannot find anything wrong with my computer. I am so frustrated, because I know what I had experienced with this computer.
Here is some additional information about my laptop. My screen resolution was once higher than recommended after using Yahoo Mail. Yahoo Mail told me my screen resolution was too low, and Yahoo Mail increased my screen resolution. The high screen resolution lasted for about a day before going back to a lower screen resolution (lower than recommended). Once after setting my laptop back to factory setting, my screen resolution was 1366 x 768. After about six hours, the screen resolution went back to a lower screen resolution (lower than recommended). Can anybody help me figure out what is wrong with my computer?