I can't bypass startup password on laptop

[GCG_admin]

Hi all

In advance, thanks for looking at this thread and apologies if posted elsewhere (I could not find one relevant) .

I have entered a password in the BIOS settings (can't remember which one) and now have forgotten it . Each time I switch the laptop on, after a few seconds of loading windows the laptop screen turns black and asks for the password.

I have a DELL Vostro 3700 running Windows 7 Ultimate.

As an amateur I tried the following so far:

1. Trying every password I know
2. Pressing F12, F2, F8 on startup
3. Trying a fresh install of operating system
4. Booting off my network
5. Currently taken the screws off the laptop with a view of finding an internal battery to take of to reset (this is where I stopped myself)

Please help! I have a new member of staff start tomorrow and I need the laptop working!

Thanks