Manual says press Del key during startup and then F8 to restore failed bios. Not sure if this is in your particular motherboard as their naming schedule is drop dead stupid and some of these versions have dual bios and some don't.
K8N, K8N-SLI, K8nXP-SLI, K8N-Ultra, K8n-Prohttp://america.giga-byte.com/FileList/Manual/motherboard_manual_ga-k8n(pro)(ultra)-sli_e.pdf
Tech support numbers at the bottom of pdf if necessary. Good Luck!