sometimes bad dvd drive or ram will do this. on dell laptops.. hold FN key and press power to turn on.. diagnostics boot.
A good way to check if its the ram is see how many boards you have and take one out and start up the computer , then swap to the other or see if you can find another board... failing that plug your HDD into another system and see how its health is in the computer. The last option i can think of is as above see if its the DVD drive by disconnecting it from the system and check if the computer can boot fully. IMPORTANT Take caution when working inside a system , you could damage the hardware or get a bad shock... read up on how to work with hardware or get someone who can do it properly.
remove the CMOS battery from under the keyboard on most units make sure to remove the ac adapter and battery and with everything unplugged hold down the power button for 30 seconds reassemble everything and the passwords should be gone
Agree 100% This is called POST (power on self test) The bios checks for video, memory, drives etc at boot time.....