Task Scheduler service can’t start

I have set a task in Scheduled Tasks of Win NT4. It used to run a batch file. But the Task Scheduler failed to start since last week. I tried to start it manually but I can’t. It has 2 event logs said “Timeout (120000 ms) waiting for service to connect.” (Event ID:7009) and “The service did not respond to the start or control request in a timely fashion.” (Event ID:7000)
The Technet said it can fix by install most updated Service Pack but my SP in NT is SP6a already.