The fact that you get issues not only in MSFS but with other applications as well (armory crate) is a strong hint, that this is hardware related.
Best case would be, that you didnt plug in the card good enough. Rwmoving and re-inswrting it might help.
Second best guess is, that you allrwady been underpowered and with adding the new storage, your GPU is no longer getting enough juice to operate properly. What is your PSU?
Worst possible cause i can think of: either the Slot or the pins on card got damaged while taking out or putting back in and either your mainboars or your GPU might need to be replaced.
But what I can twll for sure, when other Apps are effected as well: it is not caused by MSFS