As mentioned above, the PSU is more than likely the cause, this chart
shows the recommended PSU watts for a 460 is 500w and the 9500 is 350w.
Even though his PSU is a 550w it is probably not supplying 500w. With cheap PSU's the power output decreases over time due to cheap components. I would start with replacing this, if he can borrow one from someone else to test with it may save him money buying one and finding out that it is not the problem.
Cheap PSU's cause the most unusual problems.