I am presuming you have tried <F8> to start in Safe Mode?
You don`t say whether the keyboard and mouse are wired (PS2/USB) or wireless. If they are wireless you could try using wired items - I suggest PS2 rather than USB in case the USB ports are disabled.
Failing that I am a bit stuck unless you can use the <delete> button and get into the BIOS and try to check boot options there.
Whether resetting the CMOS by removing the battery would help I doubt but I`m sure someone here will know.
I think your best shot might be to put the drive into another PC and save everything you need and then do a reinstall.
For the future, get your daughter to shut the PC down rather than leave it in Power Saving mode for a quick start up!!