Can you overclock on a dell motherboard and can you unlock the BIOS?
I just want a pretty straight-forward answer, can you overclock and can you unlock?
Short answer: no.
Slightly longer answer: You can't unlock the BIOS, or use it to overclock, but in some cases it's possible to use something like SetFSB to overclock. However this is a dangerous method, and not recommended unless you know exactly what you are doing - it is very easy to destroy your motherboard using that method.
So basically no, you can't unlock the BIOS or overclock
Which Dell motherboard? Different ones have different limitations and some overclock very well. But not through the BIOS.
See "How to Overclock Dell BTX Computers" in Tutorials.
The E520 in my sig. is a good example.
OK it's an XPS 430. It has a 95W CPU limit, and runs 1333fsb. 45nm 3xxx Xeons work. The simplest solution is a Q9650 which scores 41% CPU at userbenchmark.com. It has room for a 2 slot wide GPU. It also has an X48 chipset which supports 400fsb, but OEMs can lock this out at the PLL chip. I would suggest trying a 333 to 400fsb tapemod on your existing CPU and see what happens.
Heatsinks on the VRM MOSFETs always help especially on a 3 Phase motherboard. Q9650 @ 400 fsb =3.6GHz. Other than that SetFSB or Clockgen software PLL mods would be about it. Results will be limited unless you raise CPU Voltage also by a VID pinmod. This would also be required for the 400FSB mod. T9303 cooler if you don't already have it. Avoid Radeon r9-3xx (and 285) and newer GPUs they won't display the Dell BIOS screen.