P.C. Motherboard

Question

P.C. refuses to boot. After 4weeks stopped booting with a check sum bios error. Have cleared cleared RTC RAM . The battery was only showing 1.68 Volt so have changed it.Still will not boot into post. This motherboard (Asus P5KPL-VM) was purchased 14th January 2008, the manual with it is revised edition V2 September 2007.