Without seeing exactly what you mean by "vertical stripes" - it's a bit difficult to comment.
Most of these type of artefacts are graphics card related.
So - first try your monitor on a friends system - and vice versa if possible.
If it's not the monitor, take out the graphics card (if there is a seperate one), clean the connector (rub lightly with an eraser) - fit it firmly back in the slot.
Report what happens.