Photoshop CS6 Font Error

Recently, some of the fonts that I've been using for years started to not work, usually, even when there's fonts that doesn't show the sample text preview, I can use it, and there's usually only one or two fonts that don't display their sample texts, but now, there's been a significant increase in these blanked out fonts and it's driving me insane that I can't find the solution to it-

I've tried deleting the font cache but it still doesn't work, and I know for sure it's not the font that's corrupted because even the bog standard fonts like system, symbol and ms serif can't be used. If I do try to use it, this happens:

I'd be very grateful to anyone who knows how to solve this problem because I'm dying slowly here.