I turned my Toshiba L305-S5891 and the screen went

If you are able to, and are diy, remove the small circular backup battery, With battery out, bootup. Removing the battery should blank any data that is causing the error.

Should you suceed, to start and run to logon wins, run to complete setup, then closed down, Reinsert battery, this also runs the clock, so you will have to reset date/time etc.

I hope you had sense to backup to independant backup device?

Action: start the computer and ress the f8 key again and again and select the option "safe mode with networking" if you get.

restore the computer on the previos day , other wise you will have to repair the operating system.