What's the name of this vertical line
The "caret". But most people call it "text cursor" or something similar.
how can I fix this problem of it disappearing in the middle of my typing.
Lots of different processes can interfere with this. I'd hazard a guess it's fine in Safe Mode, so try disabling items that auto start (e.g. using
AutoRuns) until you find the culprit.
Certain hardware may introduce drivers that cause this problem, notable docking stations for laptops. Is this true in your case?