I think, somehow she's corrupted the boot sequence of the HDD or the BIOS.
Two things to try.
1. As the PC starts up keep pressing DEL untill the BIOS screen appears then load optimal settings. If the Bios screen does not appear the BIOS is corrupted and you may need a new motherboard. Some PC's use another key to access the BIOS but it is usually DEL.
2. Start up the PC with a Boot Disc.
If neither of these work perhaps some of the other guys will have a few ideas.