Cannot Be Loaded Or Reinstalled

My younger sister was playing on the "Neopets" website. She loaded up a browser-based game called "Shenkuu River Rush". As I understand, to do this, she needed to download the "3D Life Player". The game worked fine for a while, but then started to run slow, so she restarted the computer. When she restarted, it still ran slow. She was also running the latest version of MSN/Windows Live Messenger. Finally, she loaded up the game and the computer pretty much froze (impossible to do anything, and showed no signs of resolving) so I came and shut it down manually.When I switched it on again, the computer went into the usual "We apologize for the incovenience, but Windows did not start successfully." screen. Thinking nothing of it, I selected "Start Windows Normally" and hit enter. The screen stayed on the Windows XP loading screen for a while, then flickered to a BSOD (I couldn't out what it was at this point) and restarted. This time, I selected "Last Known Good Configuration", and the exact same thing happened. I then tried running it in Safe Mode (both regular and command line)

The computer came with Windows XP loaded on it (I think it might've been Home Edition?), but I had a Windows XP Professional disk so I booted up from that. The "Windows Setup" screen comes up, and at the bottom of the screen, as is routine, the "Setup is loading files..." message is present. Just when all the files are seemingly loaded, and the message at the bottom of the screen flickers to "Setup is loading Windows.