We put a new belt on deck but the belt is real loose and the blades do not engage, it's really hard to engage the blades as well . Model 28928

Hi,
That is not a valid model I know of. Many Craftsman decks have a bushing that the engagement pivots on. Rust, dirt or corrosion at this point will keep it from engaging and will make moving the lever to engage difficult. Look for the bolt and nut that hold the pivot together.
Peace,
Clarke