Me will not boot

A friend have a PC with Win98 upgraded to WinMe. She left it for her daughter to play on. On her return there is a message “system integrity has change” on the screen. She chose an option to repair and then shut down the PC. The following morning she tried to open the PC but get the message “Invalid system disk, please insert correct disk…”. I’ve tried the scanreg /restore and fdisk /mbr routine without success. Is there any other way to recover her valuable files?