Yesterday, after coming home from work, I turned my laptop on from the sleep mode and got an error message saying "Operating system not found." However, after pressing any key, Windows properly begins the process of resuming. Additionally, when I rebooted my computer today, I got an error message saying "NTLDR not found" quickly followed about the OS error message. Again, pressing any key results in the resumption of the Windows. This is a Dell XPS 15Z running Windows 7. Does anyone know what the issue is and if I should be worried?