Can’t Access BIOS on my Compaq Presario

I can’t seem to get into my BIOS Setup. Earlier I used to do that with the F10 key but lately it is not working for some reason. I checked my laptop keyboard and it seems like the key is working fine in windows, tried disconnecting all the external stuff like external mouse and speakers and then trying, also tried connecting a mercury external keyboard but still no luck. Something has changed that is blocking me from accessing the BIOS.
I am using a Compaq Presario 5333CL with windows XP Service Pack 3. The startup screen also tells me to press F10 to enter setup.
