In this tutorial I will list all the shortcuts from all of the manufacturer to enter BIOS/CMOS. So here we go:

To enter BIOS during boot up:

• Hold down the "Del" key (AMI and Award)
• Hold down the "F1" key
• Hold down the "F10" key

To enter the BIOS from DOS promp (NOT from inside Windows):

• "Alt" + "Ctrl" + "Esc"
• "Alt" + "Ctrl" + "Enter"
• "Alt" + "Ctrl" + "A"
• "Alt" + "Ctrl" + "S"

Others:

Acer: "Ctrl" + "Alt" + "Esc"
AST, Advantage, Award, Tandon: "Ctrl" + "Alt" + "Esc"
Compaq: "F10" (When the square is in the top right hand corner of the screen)
Dell: "F1" or "Del"
Dells: Some require pressing reset twice
Dells: "Ctrl" + "Alt" + "Enter"
Gateway 2000: "F1"
Hewlett Packard: "F1"
IBM:

• Older Models: hold down both mouse buttons during boot up.
• Aptiva: "F1"

IBM PS/2: "Ins"
Some PS/2s (ex: 75 and 90): "Ctrl" + "Alt" + "?"
Some PS/2s: "When pointer at top right of screen" + "Ctrl" + "Ins"
Leading Edge (Fortiva 5000): "Cntrl" + "Alt" + "A" OR "Cntrl" + "Alt" + "S"
NEC: "F2"
Packard Bell: "F1" OR "F2"
Phoenix: "Ctrl" + "Alt" + "S" OR "Ctrl" + "S" OR "Ctrl" + "Alt" + "Ins"
"Sharp Laptop 9020": "F2"
Sony: "F3", then "F2", OR "F1"
Tandon Computers: "Esc"
Tandon: "Ctrl" + "Shift" + "Esc"
Toshiba Laptops: "Toshiba Utility"
Toshiba: "Esc"
Toshiba, Phoenix, late model PS/1 Value Point and 330s: "F1"
Olivetti PC Pro: "Shift" + "Ctrl" + "Alt" + "Num Pad" + "Del"
Miscellaneous PCs: "Ctrl" + "Esc" OR "Ctrl" + "Alt" + "+"
Zenith: "Ctrl" + "Alt" + "Ins"