There are three things you should inspect, mirror focus screen and viewfinder. Check this link, to clean your DSLR

You view is blurry because you need to Calibrating the Diopter on Your Camera

While doing this, start to adjust your viewfinder. As you dial in the + or -, you'll start to see the focusing points become either blurry or sharper. - When you believe that the focusing points are their sharpest, you've successfully calibrated your diopter. Now you can put your lens or body cap back on.

Instruction for the viewfinder

There are three things you should inspect, mirror focus screen and viewfinder. Check this link, to clean your DSLR

You view is blurry because you need to Calibrat the Diopter on Your Camera

While doing this, start to adjust your viewfinder. As you dial in the + or -, you'll start to see the focusing points become either blurry or sharper. - When you believe that the focusing points are their sharpest, you've successfully calibrated your diopter. Now you can put your lens or body cap back on.

Instruction for the viewfinder