I would second anon1's advice, try a different keyboard and make sure its not plugged into a USB 3 port as they need drivers from the OS to work, your BIOS will not be able to read anything connected to your USB 3 ports.
Another question for you ... when you start your computer and cannot get to your BIOS does windows still start correctly?
Also please post your system specs, it will help us alot (aka, processor, motherboard, ram, etc.)