How did you 超頻 your

Sempron 2500+? Did you just simply increase FSB? Did you check the
APG/PCI ratio? Do you know if your memory can handle that FSB? It
the CPU cooling good enough? Sometime the motherboard itself cannot
handle extreme overclock. You can try to decrease FSB a little bit
and make it stable. Then increase FSB 1MHz at a time until you can
not reboot you machine. The last good point is normally the limit.