A pinched wire to the micro reverse switch perhaps is why the blades won't run up w/o killing the engine- except in MIR mode? These are more complicated than they need to be, so please be precise in your description if this problem isn't new. It seems that you are saying that it was having a difficult time cranking before and that was the only issue until now? Have you had the battery actually load tested?

No I didn't load test the battery. Just checked voltage. That will be my next step. My grandsons high school football team is playing in the State Championship at the Superdome tomorrow so it won't be this week end. I actually was thinking it was the switch because it won't do anything when I twist the key but works to shut the machine off and work in MIR mode when I start it by crossing the solenoid posts. Thanks for the reply. I'll post results early next week.

For various reasons it took a little longer than I thought to get back to this. I replaced the battery with a fully charged new one. Nothing when I turn the key. I am unable at this time to see if I can cross the solenoid posts and start it. Thanks for following the thread.

As tom noted, a pinched wire can be the culprit - even the starter solenoid itself can be bad... also the switch. If you've left your machine outside or wash it in a serious way - easy to get corroded wires.
Will take a bit of troubleshooting and circuit tracing to find/fix. ..
Good luck

Batteries fail in 2 scenarios. New & used.
New ones are bad far more often then one would expect.
A load test would eliminate that possibility.

'I am unable at this time to see if I can cross the solenoid posts and start it'.
???? Did you lose your vision?

I guess I did phrase that rather badly. Actually due to illness and inclement wx I am unable to get to the machine. When I do I will do a load test and look for corroded wires. Eyesight, unlike mower, is OK.
Thanks guys.

A follow up: I broke down and took the machine into the dealer and they dianosed the ignition switch as bad. I thought I had eliminated it by taking it to them for testing. They said it was OK. I'm a little peeved that I had the switch there and could have replaced it in a matter of minutes. I had to re install it anyway. Thanks for the suggestions.