By batteries, do you mean the CMOS battery? If you haven't removed the CMOS battery, try doing so for at least 30 seconds and putting it back in. See if it lets you in then. If not, I would recommend either updating or re-installing the BIOS from Dell's website, as it may reset the bios and allow you back in. Just make sure that you have everything backed up, as there is always the chance that doing so could brick the darn thing. If that is a no go, I'd contact Dell's technical support and see what they have to say. Usually they have a specific work around for such matters that at least I am unaware of.