Diagnosis
Loss of power. This is typically a worn drive coupler or a failing motor capacitor, not dull blades.
How to Fix It
First, check the drive coupler (part 61094) as described in the grinding noise fix. Stripped teeth cause slippage and weak spinning. Replace if worn.
If That Didn't Work
The motor's start capacitor, which provides the initial torque, may be failing. This is a small cylindrical component inside the base. It requires soldering to replace.
Heads Up
Blades are not typically the issue. Do not try to sharpen them. They are not designed to be sharpened and you risk injury.