Are you just trying the DEL and F8 keys?
I've found a variety that seem to work....
On my mother's HP it's F10 that kicks it into bios...
I've also found that F1 and F12 works on the gateways at the college....
and I once ran across a slap-dash computer that required me to hit the TAB key to get rid of the splash screen and then F6 to get into the bios....odd thing.
Anyway, like the man said, if it ain't working check the manual. If it isn't there bang the keyboard repeatedly with your head during boot up and I'm sure you'll run across it....