Why after putting back together am I getting folder with question mark

My daughter about 4 months ago had a friend spill coke on her laptop. Keyboard stopped working. Took apart the laptop to clean up keyboard. Put laptop back together and it went to the sign in screen. I left it on that screen so she could login. In the morning when she tried she said it would not power up. I tried it and yes it powered up but gave me a notice, "you need to reboot" I did and now all we get is a white screen with a folder blinking and a question mark in the middle. When I start it up I get the Apple "chime" then the flashing folder with a question mark.

Have tried all the standard procedures, ie. reset PRam, start with the X key, start with the option key, start with the C key, etc.

I have not tried the boot disc as I am afraid I will loose everything on the drive. Does anyone have any other suggestion on this problem. I appreciate all the help I can get.