Keyboard and mouse not responding during POST

Hi, my PC (Acer Aspire T690) does not see my keyboard or mouse during Power On Self Test. Once Windows (Vista) is up, everything is fine.
The keyboard is connected to the USB port, but I tried another keyboard using the PS2 port, same result. I should be allowed to hit “Del” key to enter BIOS setup, but the only reaction I get from the PC is a small noise sounding like weak “tics”. ANy idea someone ?