See no POST screen and no entree BIOS

[Toyota]

Hello

I was visiting a friend en he wants to change his onboard network card .He had a F.Siemens PC with a MSI i 845 mobo.
The POST screen flasht so fast away for to show which key i must press for enter the BIOS
Ik was stupid and i press the key F1,F2 ,F10 and delete .
The first time i came in to the BIOS for changing the setting ,but later i wants change the setting to default and i saw a black screen till the windows screen flash up and everything works fine but it was not possible anymore to go in to his BIOS .
I try every key but nothing happens .
Clear the cmos and get out the battery for a while
I think i lock the BIOS and maybe here i find the solution

Sorry for my bad englisch

Eric

[edwin]

unplug keyboard, power up. when it asks to press a key to continue or to go into setup, plug in keyboard and choose the setup key.