"Media Pending", Lagging and not playing

1. In the Media section most of my videos it says  “media pending” when I select a video.
2. When I play my sequence nothing happens, the video goes black, it doesn’t show time passing in the video, and once I play it I can’t stop it.
3. Overall everything is lagging

So this has been happening all day and I can just wait a bit about it will work again but now it just won’t go back to normal, I’ve restarted my computer twice but I’m scared to again because of…

1. Everytime I try save my work this pops up and i have no idea what is means.

I’m not that good at premeire pro and I don’t necessarily trust its and my capablity to save the work I’ve done.

So please, help.