Daed Motherboard?

I have an Abit BH6 motherboard. As it booted one day, I noticed that the CPU had defaulted to a Pentium II 266 (I actually have a Pentium II 400)I went into setup and changed it back. Everything worked fine for about a day. Now, I can’t get it to POST, no sound, nothing on the screen. I pulled the CMOS jumper off to reset CMOS, nothing, I replaced the battery, still nothing. I looked for areset button, but nothing.