Amibios

I haven a compaq evo d300v and my keyboard will stop working I believe it is the bios because sometimes rather computer will boot and than the keyboard will stop working and the mouse will freeze, or I have same problem if I go into the setup utility,keyboard and mouse stop working after a while, I have replaced the motherboard battery.

Sounds more like the motherboard itself is starting to die,
or the harddrive

As Spyware Doc posted in another thread, test the memory with memtest.