“Error reading operating system”

Last week my friends computer went down, and the only response the computer would give was “Error reading operation system”. I simply thought it was the small battery. So I changed it and when I rebooted the computer I recieved an option to F1 Boot or F10 Config. When I hit F10 the computer went to a blank screen and read “Starting MS-DOS” then it read “Bad or missing Command Interpreter”. I rebooted again and hit F1 and the computer then went to a blank screen and once again read “Error reading operating system”. Has anyone ever seen this/any suggestions?