160 lawn tractor won't start?

Last summer, sometimes when turning the key - nothing would happen. Then we'd try again, and it would turn over. (Figured something was going bad). In the fall we had it worked on. They said it was the battery, and replaced it, and did a tune-up. It worked fine plowing all winter. Yesterday, we started it up, then put the mower deck on. Then, it wouldn't start. Have tried it several times, nothing. No click, nothing. Have checked all safety things (pto off, brake off, in neutral) and have checked to see that the mower deck is on correctly. We're thinking it's electrical. Any ideas? Thanks.