How blurry are we talking here? It could look a little less crisp than the DVI monitor, but blurry? It shouldn't be.
Do both monitors have a DVI and VGA slot on them? If so great...
Can you use the monitor that is blurry in the DVI slot? If so is it fine, or still blurry?
If its blurry its a problem with the monitor.
Does the monitor that doesn't look blurry, look blurry if you plug it into the VGA slot?
If it does look blurry then its a problem with the VGA cable, or the VGA slot.