Mac Mini -- two crashes in the past week

not really indigo-specific (other than the fact that this mini only runs indigo), but i thought i'd ask here for advice.

My 2012 Mac Mini I5 was just upgraded by me from 4gb to 16gb a couple of weeks ago. Just before that I upgraded to Mojave. This same mac has been sitting in a closet since 2013 running only indigo, and has been problem-free.

twice since then i've notice my indigo iPhone app did not connect. when I got home today, the screen showed the file/question mark flashing icon. I think this is boot record or HDD related.

Any guesses if this could be related to the new memory? Or does the folder/? icon indicate HDD issues? I ran disk utility first aid and it finished with no messages.

I've been looking for an excuse to put in an SSD, but i want to make sure the spinning HDD is the issue.

any thoughts?

thank you, i just ordered an SSD.