doh computer screen

This happens to me sometimes I usually use explorer so if your using explorer go into tools and then go to zoom and put it back to the original setting which will probably be 100%
 
Sounds like you've sorted it, and it might be browser specific, but on mine (Chrome) CTRL and - make it smaller, CTRL and + make it bigger, and CTRL and 0 reset it to default if you can't remember how much bigger or smaller you've gone.
 
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