Try one thing. Take out the CMOS battery from the motherboard. It is about the size of penny and its colour is shiny silver. After taking it out, turn your PC ON and goto BIOS setup. Now exit wihtout save and turn your PC OFF. Now put the battery back into its orignal place. Also check if the battery is slow, replace it with new one.
After putting it back, goto to BIOS setup and load BIOS's default settings and then 'save and exit".
I do hope that this will solve your problem.
D Wahab