The machine was so slow it seemed as if installing a simple anti-virus tool was going to take me an entire 40 hour work week. I attempted to run AVG, Avast, Malwarebytes - but all for naught.
When the machine would boot the CPU was pegging out at 100%, causing the GUI to be nearly unresponsive. Recently I came into a client who had a Windows XP machine that contained a nasty little virus that rendered the machine nearly unusable.