You could try a couple of things. One: open up the back cover under which you will find the hard drive, the memory, and the CMOS 2032 battery. Carefully remove the battery, I've seen folks mangle the battery holder my trying to pry it out from the wrong end. Keep the battery out for a few minutes (no idea why really) and then replace it in its holder. Carefully again. If unsure about any of the battery steps I'm sure there are several videos on YouTube to tutorial you through the process. This might reset your BIOS. At least it's supposed to. Check and see. Two: Clear the CMOS jumper as described on page 195 of the Acer Aspire 5742 manual with pictures. This is pretty sure to whack the BIOS password.