Dell optiplex gx260 cpu compatibility?

so i updated the bios and everything to A09 and i need to know what cpu i can upgrade it to before i go and buy one. i tried a 3.0ghz with a 800mhz FSB but nothing just turns on but doesn't boot. so i need to know what pentium 4 i can put into it. it used to have a 2.4/512/533fsb