My lenovo g580 wont boot up unless i turn on and turn off the power button

First of all, you need the present password. Then straight after turning the computer on you press F12 or insert multiple times after each other. That way you will stop the normal boot and enter the BIOS settings. There you most likely will be prompted for the password and then under security you can disable or change it.

Sounds like a bad monitor or ram. Does the hard drive, fan etc make noise when first turning it on?

If there's noises indicating it's working, it's probably a hardware issue.

Hold down the Fn button in the lower left and the press f6.
Leo

I would reinstall the keyboard and mouse drivers to be sure.

Lenovo Support Drivers Software US

Are you holding the button for a few seconds? Open Control Panel , Power Options, set to High Performance, Change power plan, advanced power settings, Scroll through and set to your preference. Button, Lid options,

I had this problem, I took it apart and cleaned my power button with alcohol. It had a sticky residue on it that was causing it to stay engaged sometimes, causing it to power on then off after 2 secs.