Check your battery’s charge level indicator, ensure the battery is fully charged.
Check the battery is seated correctly in the tool.
Make sure the battery isn’t hot. RYOBI batteries have overheat protection built into them. If the battery is too hot, the tool will not start until the battery has cooled.
Check if the chain brake is engaged because this will prevent the chainsaw from running.
Make sure the chain is tensioned correctly. An over-tensioned chain can engage the overload protection in the tool.