First impression suggest that there is a fault with the graphics card. If you have a spare card replace it and try turning the computer on.
If the problem persists try removing the CPU and see if you get post beeps (you must have a internal speaker connected to the motherboard).
A blinking vertical line is a cursor.
A caret or an insertion point
cursor
The blinking vertical light is called the cursor, I-bar or Insertion Point.
The blinking vertical light is called the cursor, I-bar or Insertion Point.
The cursor.
cursor
Insertion point
insertion point
cursor
No, It is insertion point
It indicates where the "cursor" is: that is where the next character will appear.