It is not the power draw.

coius, clean the dust out(make sure to get the PSU), attach a temperature probe to the CPU heatsink, ensure the heatsink is mounted well.

If that does not work.. *shrug* perhaps try disconnecting the Audio/Monitor Subconnection Assembly. The revised ones interfere with radeon 7000, perhaps certain versions of the rage 128 as well? A Rage 128 should work just fine without any issue at all though.

What is the ambient temp(in celsius) where your 6500 is coius?