Why all of a sudden it starts in password screen

Not sure what you mean by Password Screen, but what may help is to press F12 after turning the computer on, this should bring up a menu, your best options would be Diagnostics or if you see either Boot Manager or the model of your hard drive. Diagnostics will test the hard and show problems. If the hard is listed (either above or just below IP4 and IP6 options) then see if selecting that will get your computer to boot. Another option is to go into BIOS settings, you can check to see if there is a BIOS password, you will need to know the password to disable or change it. Make sure you do not have any CD/DVD in the optical drive or any USB drives connected.