Q: my mac book pro is showing a white screen with flashing ? on start up

See that topic of

About the screens you see when your Mac starts up - Apple Support

It means that a startup/bootable device can't be found.

If the action in the link do not solve the problem:

- Boot to recovery

OS X: About OS X Recovery - Apple Support

and repair the startup disk

- Next reinstall Yosemite via Recovery

OS X Yosemite: Reinstall OS X

If you can't repair the startup disk the means the disk failed and has to be replaced

This is the Mac Pro desktop forum. I requested your post be moved to the MacBook Pro laptop forum.