My 9-year-old Vostro 270s has some issues lately. One of them is that the screen suddenly turns to a black screen and the screen shows the previous content but in a lower resolution a few minutes later. This issue has occurred for one or two months. Yesterday, it turned to a black screen again and stayed on a black screen until I rebooted the PC. I have tried to address this issue by running hard drive defragmentation and software updates without any improvement. I can't see what else I can do to resolve this issue. Any solutions?