I have a Lowe's MTD mower. The blades will not engage.

Have you checked the usual? Deck belt, cables, etc.

Have you checked the usual? deck belt, cables, etc.?

I replaced the deck belt. No change.

Ok, (don't have a mtd right here to go out and check so... )
I'd check (manual blade engagement right?) to make sure the linkage and or cable is not broken itself... (should move the engagement pulley down on the deck) make sure no grass, etc is lodged anywhere.

Is it an electromagnetic engagement? Meaning is it a switch that engages or a lever?

I have a Lowes MTD mower. The blades will not engage.
Check to see if the belt or belts are loose and perhaps worn.

I replaced the deck belt. No change.

Check the engagement method. Some newer models will use electromagnetic clutches.