How do I check if the AGP bus is locked or not?
Overclock by raising the FSB means raising all the bus frequency, that's including raising the frequency of CPU(of course), VGA, RAM, PCI slots, well we can say almost all of frequencies. To obtain the stability, you must raised the voltage too. More voltage equal more heat.
Athlon 64 clocked at 2.2 Ghz, you are using FSB 275 Mhz (i supposed). Maybe you are raising the voltage until 1.70 or 1.75v too.
AGP bus is 1/3 of FSB, so it's mean in normal FSB (200Mhz) is 66 Mhz. from 275 MHz mean your AGP bus is 91.67 MHz. That's way too much and too dangerous for your AGP card.
try to lower your FSB bus or stop the OCing, then see how is the temp.