That could be a number of things from HDD failure to something else. Not sure what it could be..
Short of downloading a another OS and booting from a USB to see if a file is missing not sure what else you could do.

So im not sure what my sisters did to my tower, normally they play no$GBA to play pokemon firered, my sister went to turn the computer on and what happened this time was odd, I've had it happen before and fixed it (note this was last summer and i have the crappiest memory) but each time i start it would load as normal but it would give me the option to boot safe mode ect. so i choose all the options, held F8 and went from the option that boots off the last good configuration and it had no luck, I said 'sc**w this' and pulled out my windows XP CD and put it in, it booted off the CD but when i went to reinstall on the system it said the CD isnt in the CD drive, is there another approach i could take?
Well last known good config just means it's going to load the last settings that got you to the windows loading screen. It doesn't always mean it's going to work.


[ATTACH=CONFIG]30694[/ATTACH]
This is where it reboots