Help! Can't Startup Blinking Underscore

I have a Latitude D630 that I upgraded to Windows 10 like a year ago. It always worked great, but last night I shut it down via holding down the power button and today it won't start up. All I get is a blank screen and a blinking underscore. I got into the boot menu and ran diagnostics and no problems came up. I've looked at at least 10 other posts about this and nothing fixes it. No idea what to do, any help would be appreciated!