How old is the belt? Are you checking the "looseness" with deck raised, or lowered? Belt will be a bit tighter when deck is lowered, and that's where the work is done, so if the belt is not slipping (you can see, hear, feel.....the blades slowing or stalling) when you mow, you're probably OK.
If the belt is more than 3 years old, look for cracks on the V side of the belt. If you find numerous or deep cracks, replace it, it is stretched out.
If the belt is new, is it the OEM replacement belt?
Aftermarket belts can be a tad longer or shorter than the OEM spec dimensions, requiring adjustments in some cases.

I did feel a few cracks in the belt and it's 5 years old.
When I would disengage the blades it would make a long whine or screech sound for a few seconds until it stopped turning. Does that mean the clutch has worn out and is finished?
When I pull the knob out to start the blades, it doesn't make a click sound so I am thinking that it's a problem with the wires or a plug. I want this to be an easy fix so I won't have to pay someone to replace expensive parts.