Luckily it is an older laptop. There are different ways of doing it.
To reset the bios in an Acer 5100 you need to remove your DDR2 memory sticks, below you can see "j2", it is a 3 pin jumper close to the battery look which 2 of the 3 pin it is on, then move the little plastic tab from those two to the other two pins and then hit the power button once. When you have done this, return the tab back to the original setting. This should reset the bios. Should that not work, you can take more drastic steps and follow the thread here by a user name Robinhood69. It is very involved but should work as well. the other way is to obtain software BIOS/CMOS password recovery tools and yes Zain's flashing of the BIOS would also do it....Good Luck and let us know how it is going.