[Darkjedi]

That's very very vague. It might be caused by some software conflicts of some stuff you installed. Or the files you are trying to open are incompatible or have weird code, very large. Try making a new excel sheet, save it with like a couple cells filled out and see how long it takes to open.

Short of that, and you can't figure out the piece of software causing the conflict, you can always try hard resetting.