Armada 7800

I have a Compaq Armada 7800 for repair. Ive tried all the usual key combos for the BIOS, but cant get in for love nor money.
Compag say its F10, but its not doing it. Anyone know of any odd key combos to get in, or is the mobo knackered, and thats the cause of his boot failure anyway?

F10 only when the cursor is flashing at the top right hand corner.

Yep, tried it thx NooNoo. Motherboard duff anyway - wont recognise anything, so its a bin job.