Do you really think anyone can help you with all this info you hAve gave us?
Push mower ?
Riding mower?
Model number and or size , year made
Any kind if info to let us know what you are talking about.
Will it go in reverse when pto not engaged.
Does it shut down with blades engaged when you try to backup ?
Did this just start or has it always done this?
Like said earlier post we don't know what you have. You will find in most of the modern riding mowers they have a reverse safety switch that won't let them mow in reverse.