There are jumpers on the motherboard for doing just that, but if you can't find them (should be the same as the 'password' jumper referred to in the manual above), then you can remove the battery for 10-20 seconds, unplugged from power, while holding the power button down.  
My old print server (W2K3), a PE 830 had three SATA drives.  I removed two as they would not be needed for setup as a Windows 7 desktop. No where in the Bios (A04) can i find a set to factory defaults or allow me to tun off SATA 1 & 2, just Auto & na. so whenn it boots every time I see "SATA Port 1 hard disk drive not found" as well as Port 2. Press F1 to continue and F2 to enter setup, very annoying.
PE 830 Conversion to Windows 7