weird error prevented access to .exe's and now prevents boot up

I have windows xp running on a machine in my office - it is rarely if ever used. I have an external drive hooked up onto which i back up my other laptops over wireless, and sometimes i will google some things. apart from that, it just sits. msi, windows updates are both automatic. this morning i try using it and i get some funky error when i try opening firefox, regarding DLL's and applications that are not valid.... didn't think anything of it and figured a good reboot would take care of things. Apparently my machine already saw that coming and screwed me even harder by giving me this error message and preventing boot up. i tried repairing windows with the cd, but nothing changed, so im currently restoring an image (thank god i made one) and we'll see if that works... anyone know this is about and if its going to happen again? I have a second machine running EXACTLY the same everything (except hardware) and it so far has not exhibited even a tendril of a problem.

error:

The application or DLL C:\Windows\WinSxS\x86_microsoft.windows.common-controls_6595b64144ccf1df_6.0.2600.6028_x-ww_61e65202\comctl32.dll is not a valid Windows image. Please check this against your installation diskette.

 

well, re-imaging fixed the problem, but i'm still interested in knowing what caused the problem in the first place so i can prevent it from reoccuring... any ideas?

 

Sounds a lot like a virus or something. I've only seen those kinds of behavior by some program hooking into the execution of programs.