My acer aspire 5551 laptop isn't starting up its

Hi

Check underneath and use a small screwdriver to open the small rectangular panel with the image of a stack of CDs near it. This is where the Hard Drive sits.

Check to see if the Hard Drive is properly fitted properly docked into its socket and screwed down or held down properly so it is immobile during use.

If this is not the problem, tap the Fn + the correct function key to enter the Boot Menu at Start Up and use the keyboard arrows to select the Hard Drive boot option.

Make sure there is no CD or DVD in the Optical Drive.

If none of these is the problem then, regrettably, your hard drive may have failed, so remove it and test it in a hard drive dock or an external 2.5" Hard Drive Enclosure.

If it has failed you will obviously need a new hard drive, bootable operating system disc, drivers disc and programs and security software to reinstall everything to the new hard drive.

Unfortunately, any data on the old drive will be lost.

It is very unusual for a Hard Drive to fail suddenly without some prior warning or signs of failing (the only realistic way would probably be through a drop, severe knock, serious mains power surge or mains power cut, incorrect shutdown procedure, or sudden disconnection of the power cable during use).

Back up regularly to an external storage device and do not ignore any warning signs. Also plug all computer equipment to the mains via a Surge Protector/Suppressor to prevent damage from power surges or fluctuations.

I hope this helps

You operating system is probably corrupt. You will need to install a fresh copy of your operating system. This will erase all your files, but i guess your computer's health is more important.