1. The race went off before the scheduled start time.
This is rare but can happen occasionally on Irish racing and a lot more often on overseas races.
2. The clock on your PC is wrong
This is by far the most likely explanation. If your PC clock is running slow, then by the time the PC thinks that it is time to place the bets, the race has already gone InPlay.
To ensure that your PC clock is always synchronised, you are recommended to download and install the free NetTime tool from www.timesynctool.com - this utility will resync your clock with an internet timesource at a user-defined interval. If you set the utility to resynchronise every hour, then your PC clock should remain accurate throughout the day.
This utility works with all versions of Windows (including Windows 10)