What's wrong with my Sportcraft TX 4.9 treadmill?

I had my Sportcraft TX 4.9 treadmill in storage at a friend's for about 4 years. I recently got it back to recooperate after a leg injury but it won't turn on. It is missing the safety key but I think any magnet of the same shape should work (not to mention the display should at least turn on without the magnet). I know it is getting power to the circut board (I removed the bottom cover to be sure & the fuse is good & there is a small green light on the circut board that comes on). Can anyone please help me???