oh crap, i thought you said 2000mhz. i now see you said 2000+, whoops. check in your BIOS the CPU external frequency should read at 133mhz if your 2600+ is the 266 front side bus version
or your CPU external frequency should read at 166 mhz if your 2600+ is the 333 front side bus version.
i am willing to bet you have the 2600+ 266FSB version and your CPU external frequency defaulted back to a 100mhz.