Media pending leading to crash

Hi all.

I am experiencing something very weird in Premiere Pro. Before I explain the problem, I should say that, although the laptop that I run Premiere on is not very powerful, it's been working just fine over the past few years regularly on projects that had a considerable duration and hours of 4K footage. 

I've just received a project from the editor for a short film I'm working on. The project opened fine, and I worked on it for about one hour before going for dinner. When I came back, I reopned the project and was greeted with "Screen 1" and then "Screen 2". Notice "Screen 2" is taken from a phone, as when I tried to take a screenshot the laptop froze and lead to "Screen 4". 

After trying clearing the cache, restarting and all the usual trouble shooting, I unplugged the hard drive (the footage is on a hard drive), and when I plugged it back in, the drive had changed letter (it was D:, now it became E:). With this done, the project now opened fine (I tried this a few time manually switching HDD letters back and forth), exept that now I have a different problem, as seen in "Screen 3". In addition, the preview seems slow, although the footage (and the time) runs fine. 

I thought I would just work on it this way, exept that tonight, when I opened it again, I am back on "Screen 1" and "Screen 2", even though the HDD letter has been changed. 

I would assume that the problem is in my hardware, but I have literally just finished working on a project that contained much more footage than this current one. Do you have any ideas on what could be causing this issue? 

Thanks in advance!